1. Thinly slice the beef across the grain into 1/4-inch-thick strips. Marinate the beef in 1 tablespoon soy sauce for at least 10 minutes. For easier slicing, place beef in the freezer for 15 minutes before cutting.
2. Trim green beans or mixed vegetables into bite-sized pieces. Mince garlic and slice scallions, setting aside the dark green portions for garnish.
3. Whisk together all sauce ingredients (honey, Shaoxing wine, soy sauce, water, garlic, and optional ginger and red pepper flakes) in a bowl and set aside.
4. Heat a large wok or skillet on high heat and lightly coat the marinated beef pieces evenly with half of the cornstarch.
5. Add 2 tablespoons of oil to the pan and fry the beef in batches to avoid overcrowding, cooking each batch until crispy and browned on both sides (about 2-3 minutes per batch). Drain excess oil and set beef aside.
6. In the same pan, add remaining oil if needed and cook green beans (or mixed vegetables) covered with a splash of water and 1/4 teaspoon kosher salt until bright green and tender-crisp, about 4-5 minutes.
7. Stir-fry the vegetables with garlic and the white/light green parts of scallions until fragrant, about 1-2 minutes.
8. Return beef to the pan. Pour the prepared sauce over and stir to combine.
9. In a small bowl, mix remaining cornstarch (approximately 1 tablespoon) with 3 tablespoons water to create a slurry. Slowly add this to the pan while stirring until the sauce thickens and evenly coats the beef and vegetables, about 1-3 minutes.
10. Garnish with scallion greens and serve immediately with steamed white rice or noodles.