Slice the steak and vegetables, keeping them separate.
In a small bowl, mix together 2 tablespoons soy sauce, 1 tablespoon sugar, 1 teaspoon cornstarch, garlic powder, ground ginger, salt, and pepper. Toss the steak in the mixture until coated, then refrigerate (marinate for 30 minutes for best results).
In another small bowl, mix the glaze ingredients (3 tablespoons soy sauce, 1 tablespoon cornstarch, 1 1/2 tablespoons sugar). Set aside.
Heat 1 tablespoon of oil in a large skillet over medium-high heat. Add the sliced onion and bell pepper. Stir-fry for 3–5 minutes until slightly tender. Remove from skillet and set aside.
In the same skillet, heat the remaining 1 tablespoon of oil. Add the marinated steak and cook for 5–7 minutes, stirring occasionally, until browned and cooked through.
Return the vegetables to the skillet. Pour in the glaze and stir for 1–2 minutes, or until the sauce thickens and coats the meat and vegetables.
Serve hot over white rice.