Marinate the Beef: In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch. Whisk until smooth. Add the beef, coat well, and marinate for at least 15 minutes.

Sear the Beef: Heat a skillet over medium-high heat, add 1 tablespoon of oil, and sear the marinated beef for about 1-2 minutes on each side until browned.

Cook the Vegetables: In the same skillet, add bell peppers and onion. Sauté for 3-4 minutes until slightly crisp.

Add Aromatics: Stir in minced garlic and grated ginger. Sauté for about a minute until fragrant.

Combine Ingredients: Return beef to the skillet, add broth or water, and simmer for 2-3 minutes until the sauce thickens.

Season and Serve: Adjust seasoning with salt and pepper. Serve hot over rice or noodles.