1. In a bowl, mix soy sauce, oyster sauce, cornstarch, and brown sugar. Add sliced flank steak, ensuring it's well-coated. Marinate for at least 15 minutes. PEPPER STEAK
2. Heat vegetable oil in a wok or skillet over high heat. Add marinated beef and stir-fry until browned. Remove beef from the pan and set aside.
3. In the same pan, add a bit more oil if needed. Saute bell peppers, garlic, and ginger until vegetables are tender yet crisp.
4. Return the cooked beef to the pan, toss everything together, and season with salt and black pepper.