In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch to create a flavorful marinade. Add the thinly sliced beef steak, tossing gently to coat. Let marinate for at least 15 minutes.

While the beef marinates, prepare the vegetables by slicing the bell peppers and onion, and mincing garlic and grating ginger.

Heat a large skillet over high heat with vegetable oil. Sear marinated beef slices for 1-2 minutes per side until browned. Remove from skillet and set aside.

In the same skillet, add more oil if needed, then sauté the bell peppers and onion for 3-4 minutes until slightly softened.

Add minced garlic and grated ginger to vegetables, stir for another minute, then return cooked beef to skillet and pour in beef broth or water. Cook for 2-3 minutes until sauce thickens.

Season with salt and pepper to taste, then remove from heat and serve over rice or noodles.