In a mixing bowl, combine soy sauce, oyster sauce, and cornstarch to create a smooth marinade. Add your thinly sliced beef, ensuring each piece is well-coated. Let marinate for at least 15 minutes at room temperature.

Wash and slice the bell peppers into strips and slice the onion into wedges. Mince the garlic and grate fresh ginger.

Heat a large skillet over high heat and add vegetable oil. Once shimmering, add the marinated beef, searing for 1-2 minutes on each side until browned. Remove and set aside.

In the same skillet, add more oil if needed, then toss in bell peppers and onions. Sauté over medium-high heat for about 3-4 minutes until tender yet crisp.

Add minced garlic and grated ginger, sautéing for an additional minute. Return the cooked beef along with any juices, stir in broth, and cook 2-3 minutes until sauce thickens.

Season with salt and pepper, serve hot over rice or noodles.