Marinate the beef by whisking together soy sauce, oyster sauce, and cornstarch in a medium bowl. Add thinly sliced beef and let marinate for at least 15 minutes.

Sear the marinated beef in a hot skillet with vegetable oil for 1-2 minutes on each side until browned. Remove beef and set aside.

Sauté bell peppers and onion in the same skillet for 3-4 minutes until softened but still crisp.

Add minced garlic and grated ginger, cooking for another minute until fragrant.

Combine seared beef and any accumulated juices with the sautéed vegetables. Add beef broth or water, mixing well. Cook for 2-3 minutes until the sauce thickens.

Adjust seasoning with salt and pepper, then serve hot over rice or noodles.