Creating Pepper Steak with Bell Peppers and Onion can be straightforward if you follow these simple steps:

1. Marinate the Beef: In a bowl, combine the sliced flank steak, soy sauce, oyster sauce (if using), and cornstarch. Mix well and let it marinate for about 10 minutes while you prepare other ingredients.

2. Prepare the Vegetables: Slice the onion and bell peppers. Mince the garlic and ginger.

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

4. Cook the Beef: Add the marinated flank steak to the hot skillet. Cook for 3-4 minutes until browned, stirring occasionally. Remove the beef from the skillet and set aside.

5. Sauté the Vegetables: In the same skillet, add the sliced onion and bell peppers. Stir-fry for 2-3 minutes until they become slightly tender but still crunchy.

6. Add Garlic and Ginger: Stir in the minced garlic and ginger, cooking for another minute until fragrant.

7. Combine Ingredients: Return the cooked beef to the skillet with the vegetables. Toss everything together and let it cook for an additional 1-2 minutes to combine flavors.

8. Season: Season with salt and pepper to taste.

9. Serve Hot: Serve the pepper steak over cooked rice or noodles, distributing the vegetables and sauce evenly.