Follow these steps to create your Pepper Steak with Bell Peppers and Onion:

1. Prepare the Steak: In a bowl, toss the thinly sliced flank steak with cornstarch, ensuring an even coating. This will help the meat sear nicely and remain tender.

2. Heat the Pan: In a large skillet or wok, heat the vegetable oil over medium-high heat until shimmering.

3. Sear the Beef: Add the flank steak to the hot pan in a single layer, allowing it to sear without overcrowding the pan. Cook for 2-3 minutes until browned, flipping halfway through. Remove the steak and set aside.

4. Cook the Vegetables: In the same pan, toss in the sliced bell peppers and onions. Sauté for about 5 minutes until they begin to soften. Add the minced garlic and cook for an additional minute.

5. Create the Sauce: In a small bowl, mix together the soy sauce, oyster sauce (if using), Worcestershire sauce, ground black pepper, sugar, and beef broth.

6. Combine Everything: Return the beef to the pan with the vegetables, pouring the sauce over the mixture. Stir well to combine everything and allow it to simmer for about 3-5 minutes until the sauce thickens slightly.

7. Taste and Adjust: Adjust seasoning to taste; feel free to add more soy sauce or pepper for additional flavor.

8. Serve: Once everything is well combined and heated through, remove from heat.