In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch until smooth. Add the thinly sliced beef steak, tossing to coat. Let marinate for 15 to 30 minutes.

Wash and slice the bell peppers into strips and slice the onion into thin rings. Mince the garlic and grate the ginger.

Heat a tablespoon of vegetable oil in a skillet over medium-high heat. Add the marinated beef in a single layer and sear for 1 to 2 minutes on each side until browned.

In the same skillet, add remaining oil if needed, and sauté the sliced bell peppers and onions for 3 to 4 minutes until tender and translucent.

Return the beef to the skillet, pour in the beef broth or water, and cook for 2 to 3 minutes until the sauce thickens. Season with salt and pepper.