In a medium bowl, mix together soy sauce, oyster sauce, and cornstarch until smooth. Add thinly sliced beef steak, tossing to coat evenly. Allow the beef to marinate for at least 15 minutes at room temperature.

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

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

Stir in the minced garlic and grated ginger, cooking for an additional minute until fragrant.

Return the beef to the skillet and pour in the beef broth or water. Stir everything together, cooking for 2-3 minutes until the sauce thickens slightly.

Taste and adjust with salt and pepper as needed. Serve over a bed of rice or noodles.