Healthy Yellow Summer Squash Casserole with a Golden Breadcrumb Topping

By:

Gabriella Brotherton

Published:

September 16, 2026

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Healthy Yellow Summer Squash Casserole

Every July my kitchen counter disappears under a pile of yellow squash, and this casserole is the recipe I reach for first. Tender sliced squash, gooey melted cheese, fresh basil, and a golden breadcrumb topping come together in one dish that works just as well as a weeknight side as it does as a potluck contribution.

You can assemble it ahead of time, keep it covered in the refrigerator, and bake it right before you leave for the party. It travels well to picnics and summer dinners, and it still tastes good once it cools to room temperature on the table.

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Why We Love This Recipe for Healthy Summer Squash Casserole

This casserole started as a happy accident in my own kitchen. I had already fallen for a healthy zucchini casserole and made it all summer long, so when the yellow squash took over the garden bed, I simply swapped summer squash for the zucchini and kept the method I loved.

That small change gave me a dish that is now requested at every family cookout.

The breadcrumbs do quiet, important work here. They soak up the liquid that squash releases as it bakes, so the finished casserole stays creamy instead of turning into a puddle, and they double as the crunchy golden layer on top. Fresh basil and a mix of Italian blend cheese and Parmesan bring plenty of flavor without a heavy cream sauce.

I serve it as a side dish, and it plays nicely with just about anything coming off the grill. On nights when I want something a little bolder, I pair it with Cajun flank steak.

When the kids are home, barbecue chicken is the usual answer. And when I am cooking for friends who prefer something lighter, garlic lemon chicken is my pick.

It also holds its own next to roasted chicken, burgers, or a simple plate of sliced tomatoes and sweet corn.

The best part is how forgiving it is. You can bake it right away, or you can put the whole thing together in the morning, slide it into the refrigerator, and finish it in the oven while you set the table.

That kind of flexibility is exactly what I want in a summer recipe, and it is the reason this dish shows up at so many of our gatherings.

Key Ingredients for this Recipe

The ingredient list is short, and most of it is probably in your kitchen already. Here is the full lineup, with the amounts I use.

Ingredient	Amount
Garlic	1 clove, peeled
Sourdough bread	2 slices, about 3 to 4 ounces
Extra virgin olive oil	2 tablespoons
Summer squash	6 medium, about 3 pounds, cut into rounds
Ripe tomato	1 small, diced
Fresh basil	2 tablespoons chopped, plus more for garnish
Coarse kosher salt	1 1/2 teaspoons, or to taste
Freshly ground pepper	To taste
Shredded Italian blend cheese	4 ounces (1 cup)
Shredded Parmesan cheese	1/2 cup

Yellow Summer Squash

You need six medium summer squash, which works out to about three pounds once you cut them into rounds. Garden squash varies wildly in size, so I weigh mine when I can and let the total weight be my guide rather than the count.

Any summer squash works here, including yellow crookneck, patty pan, or zucchini, and a mix of two or three varieties looks lovely on the plate.

Sourdough Bread

Two slices of sourdough, about three to four ounces, get torn into pieces and blitzed into coarse crumbs in the food processor.

This is my healthier stand in for the usual Ritz cracker and butter topping, and it does far more than sit on top of the dish. Those dry crumbs absorb moisture, seasoning, and cheese as the casserole bakes, which is what binds everything together.

Because the bread does that job, you do not need eggs or any other filler to hold the filling together.

I like to use bread that is a day or two past its best, since dry bread breaks into a nicer crumb than fresh, squishy slices. Pulse it just until you see irregular pieces about the size of a pea. If you go too far, you end up with sand, and the topping loses its crunch.

Cheese

Summer squash releases a lot of water as it cooks, which is why this recipe skips a cream sauce or heavy cream entirely. All of the richness comes from cheese instead.

I use four ounces of shredded Italian blend cheese, the kind sold as Italian Blend or Pizza Blend, plus a half cup of shredded Parmesan.

The blend melts smoothly into the layers, and the Parmesan brings a salty, nutty edge that keeps the dish from tasting flat.

Half of the Italian blend goes into the middle of the casserole, and the rest goes on top at the end with the Parmesan, so every forkful gets cheese in two places.

If you only keep one of the two on hand, use what you have and taste the filling before it goes into the oven, since Parmesan is the saltier of the two.

Step By Step Instructions For Making This Squash Casserole

The method comes together in four short steps, and the whole thing bakes while you get on with the rest of your day.

Step 1: Blend Breadcrumbs

Preheat the oven to 375 degrees F. Fit your food processor with the steel blade, turn the motor on, and drop the peeled garlic clove through the feed tube so it minces.

Remove the lid, tear the sourdough into three or four pieces per slice, and add them to the bowl. Cover and process until the bread forms coarse crumbs. With the motor still running, drizzle in the two tablespoons of extra virgin olive oil.

That is the entire prep for the topping. From here the crumb mixture pulls double duty, soaking up liquid from the squash and later turning into the golden crust on top.

The crumbs will look a little damp from the oil, and that is exactly right. Damp crumbs cling to the squash and brown evenly instead of scattering across the dish.

Step 2: Combine Ingredients

In a large bowl, toss three quarters of a cup of the breadcrumb mixture, which is about half of it, with the sliced squash, the diced tomato, the chopped basil, the salt, and the pepper until everything is evenly combined.

Step 3: Assemble Casserole and Bake

Coat a 9 by 13 inch casserole dish, or any dish of similar volume, with cooking spray. Spread half of the squash mixture in the bottom. Scatter half of the Italian cheese blend over it, then add the remaining squash mixture on top.

Leave the rest of the cheese and all of the breadcrumbs for later. Cover the dish with foil and bake until the squash is fork tender, about 50 to 55 minutes.

Healthy Yellow Summer Squash Casserole, Step 3: Assemble Casserole And Bake — Healthy Yellow Summer Squash Casserole With A Golden Breadcrumb Topping 24

The foil traps steam, so the squash softens all the way through before the topping goes on. That is the difference between tender squash and a dry, half cooked casserole.

Step 4: Add Topping and Bake Until Done

Increase the oven temperature to 450 degrees F. Pull the foil off carefully, since the steam underneath is hot. Top the casserole with the remaining Italian cheese blend, the Parmesan, and the rest of the breadcrumbs.

Slide it back into the oven uncovered and bake until the cheese is melted and the topping is golden brown, about 12 to 15 minutes.

Healthy Yellow Summer Squash Casserole, Step 4: Add Topping And Bake Until Done — Healthy Yellow Summer Squash Casserole With A Golden Breadcrumb Topping 25

Keep an eye on it near the end, because a hot oven can take the crumbs from golden to dark quickly.

Variations To Try

Once you have made this casserole a time or two, it becomes a great canvas for whatever is sitting in the crisper drawer. These are the swaps I come back to most.

Bell pepper: Dice one bell pepper and sauté it over medium heat until tender. Let it cool slightly, then stir it into the squash and breadcrumb mixture along with the tomatoes.
Butter instead of oil: Melted butter in place of the olive oil gives the crumb topping a richer flavor.
Extra sharp cheddar: Swap shredded extra sharp cheddar for the Italian cheese blend if you want a sharper, more classic flavor.
Mixed squash: Replace half of the yellow squash with zucchini, or use a blend such as patty pans and yellow zucchini for a multicolored dish.
Sweet corn: Cut the kernels from two ears of sweet corn and add them to the bowl with the squash and breadcrumb mixture.
Sautéed Vidalia onion: Finely slice a Vidalia onion and cook it in one tablespoon of butter over medium low heat until softened, about 8 minutes. Spread it on top of the casserole before you cover the dish with foil.

One more note on the onion version. Those sweet, buttery slices sit on top of the filling rather than mixed through it, so you get a soft, jammy layer right under the foil that contrasts nicely with the crisp crumbs above.

Healthy Yellow Summer Squash Casserole, Variations To Try — Healthy Yellow Summer Squash Casserole With A Golden Breadcrumb Topping 26

My favorite of these is the corn version in late summer, when the sweet corn and the squash are both at their peak. Whichever way you go, keep the amounts of squash, cheese, and breadcrumbs the same, and the casserole will bake in the same time.

FAQs

How do you keep squash casserole from getting watery?

The breadcrumbs in this recipe act as a natural thickener. Half of the sourdough breadcrumb mixture is tossed directly with the sliced summer squash, tomato, and seasonings before baking. As the squash releases its natural moisture during cooking, the breadcrumbs absorb the liquid, resulting in a cohesive casserole without a watery texture.

Can you make summer squash casserole ahead of time?

Yes, this casserole can be assembled up to 8 hours ahead of time. To do this, prepare the dish and keep the reserved sourdough breadcrumb mixture stored separately. Cover the assembled casserole and refrigerate, then add the reserved breadcrumbs just before baking. Reheat leftovers in the oven to restore the crisp topping.

What is the difference between yellow squash and crookneck squash?

Yellow squash and crookneck squash are essentially the same type of summer squash. Crookneck squash is a specific variety of yellow squash distinguished by its curved, swan-like neck. Both can be used interchangeably in this casserole recipe. Look for firm, glossy squash without soft spots for the best texture.

What cheese goes best with summer squash?

This recipe uses a combination of shredded Italian blend cheese and shredded Parmesan cheese. The Italian blend provides a rich, gooey melt, while the Parmesan adds a savory, umami flavor. You can also substitute the Italian blend with shredded extra sharp cheddar cheese for a different taste. Shredding cheese from a block is recommended for better melting.

Healthy Yellow Summer Squash Casserole with a Golden Breadcrumb Topping

Healthy Yellow Summer Squash Casserole

Why We Love This Recipe for Healthy Summer Squash Casserole