In a mixing bowl, whisk together soy sauce, oyster sauce, and cornstarch until smooth. Add the thinly sliced beef steak, ensuring each piece is well-coated with the marinade. Allow it to marinate for at least 15 minutes.

While the beef marinates, slice the bell peppers and onion into thin strips and mince the garlic. Grate the ginger and set the prepped vegetables aside.

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

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

Add the minced garlic and grated ginger to the skillet, stirring for about a minute until fragrant. Return the seared beef to the skillet along with beef broth.

Stir everything together and cook for an additional 2-3 minutes until the sauce thickens. Season with salt and pepper to taste, and serve hot over rice or noodles.