Creating Black Pepper Beef is simple if you follow these easy steps:

1. Prepare the Beef: In a bowl, toss the sliced flank steak with cornstarch. Set aside for 10 minutes to marinate.
2. Heat the Pan: In a large skillet or wok, heat the vegetable oil over medium-high heat.
3. Stir-Fry the Beef: Add the marinated beef to the hot pan, cooking until browned and cooked through, about 3-4 minutes. Remove and set aside.
4. Sauté Vegetables: In the same pan, add the sliced bell pepper and onion. Stir-fry for about 2-3 minutes until they start to soften.
5. Add Garlic and Pepper: Stir in the minced garlic and ground black pepper, cooking for an additional minute until fragrant.
6. Combine Ingredients: Return the cooked beef to the pan, mixing it with the vegetables.
7. Make the Sauce: In a small bowl, whisk together soy sauce, oyster sauce, rice vinegar, sugar, and a pinch of salt. Pour the sauce over the beef and vegetables.
8. Stir-Fry Together: Cook everything together for another 2-3 minutes, ensuring the beef is well-coated with the sauce.
9. Garnish: Remove from heat and garnish with chopped green onions.
10. Serve Immediately: Enjoy your Black Pepper Beef hot, preferably over rice or noodles.

These straightforward steps will guide you in creating this incredible dish effortlessly.