In a mixing bowl, whisk together soy sauce, oyster sauce, and cornstarch. Add sliced beef and marinate for at least 15 minutes to enhance flavors.

Slice the bell peppers and onion into thin strips. Mince garlic and grate ginger, setting these aside.

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

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

Add minced garlic and ginger to the vegetables, stirring for about 1 minute. Return seared beef to skillet and pour in beef broth. Cook for 2-3 minutes until sauce thickens.

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