In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch. Add sliced beef steak and toss well to ensure each piece is coated. Let marinate for at least 15 minutes.

While the beef marinates, slice bell peppers into strips, thinly slice the onion, mince the garlic, and grate the ginger.

Preheat the skillet or wok over high heat, add vegetable oil, and sear the marinated beef in batches for 1-2 minutes on each side. Remove and set aside.

In the same skillet, stir-fry bell peppers and onions over medium-high heat for 3-4 minutes. Then add minced garlic and ginger, and stir for another minute until fragrant.

Return the seared beef to the skillet, pour in the beef broth or water, and stir well. Cook for an additional 2-3 minutes until the sauce thickens.

Serve hot over a bed of steamed rice or egg noodles.