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

Sear the Beef: Heat 1 tablespoon of vegetable oil in a large skillet or wok over high heat until shimmering. Carefully add the marinated beef in a single layer, searing for 1-2 minutes on each side until browned. Remove beef and set aside.

Sauté Vegetables: In the same skillet, add another tablespoon of vegetable oil if needed and toss in sliced bell peppers and onions. Sauté over medium-high heat for about 3-4 minutes until they are tender but still crisp.

Add Aromatics: Add minced garlic and freshly grated ginger to the skillet with the vegetables, stirring well. Cook for an additional minute until aromatic.

Combine Ingredients: Return seared beef to the skillet, pour in the beef broth or water, and mix gently. Allow to simmer for 2-3 minutes until sauce thickens and coats the beef and vegetables.

Season and Serve: Taste and adjust seasoning with salt and pepper as needed. Serve hot over rice or stir-fried noodles, garnished with fresh herbs.