In a medium bowl, combine soy sauce, oyster sauce, and cornstarch to create a thick marinade. Add your sliced beef to the mixture and let marinate for at least 15 minutes.

Heat a large skillet over high heat, add vegetable oil, and sear the marinated beef slices for 1-2 minutes on each side until golden brown. Remove the beef and set aside.

In the same skillet, add more vegetable oil if needed. Sauté bell peppers and onions for around 3-4 minutes until tender and slightly crunchy.

Add minced garlic and grated ginger to the skillet, stirring for an additional minute until fragrant.

Return the seared beef to the skillet along with juices. Pour in beef broth or water and cook for 2-3 minutes until the sauce thickens slightly.

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