In a mixing bowl, whisk together soy sauce, oyster sauce, and cornstarch until smooth. Add the thinly sliced beef steak to the marinade, tossing well. Let it marinate for at least 15 minutes.

While the beef is marinating, prepare the bell peppers and onion. Slice the bell peppers into strips and the onion into thin wedges. Mince the garlic and grate the ginger.

Heat 1 tablespoon of vegetable oil in a skillet over high heat. Add the marinated beef slices in a single layer, searing for 1-2 minutes on each side until browned. Remove and keep warm.

In the same skillet, add another tablespoon of vegetable oil. Add the sliced bell peppers and onion, cooking for 3-4 minutes until tender-crisp.

Add minced garlic and grated ginger to the skillet, sautéing for an additional minute. Return the cooked beef, pour in the beef broth, stir, and let simmer for 2-3 minutes.

Taste and adjust with salt and pepper if needed. Serve hot over rice or noodles.