In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch to create a smooth marinade. Add the thinly sliced beef and ensure each piece is thoroughly coated. Let marinate for at least 15 minutes.

Slice the bell peppers and onions into thin strips. Mince the garlic and grate the ginger.

Heat a large skillet over high heat and add vegetable oil. Once hot, add the marinated beef in a single layer and cook for 1-2 minutes without stirring. Remove the beef and set aside.

In the same skillet, add more vegetable oil and sauté the bell peppers and onions for 3-4 minutes until tender-crisp.

Add minced garlic and grated ginger to the skillet. Stir for about a minute, then return the cooked beef to the skillet with beef broth or water to deglaze. Stir and cook for 2-3 minutes.

Season with salt and pepper to taste. Serve hot over steamed rice or noodles.