01 - Combine the sliced flank steak with soy sauce, Shaoxing wine, cornstarch, and black pepper in a bowl. Mix thoroughly to coat and marinate for 10–15 minutes at room temperature.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, sugar, beef broth, and cornstarch in a small bowl until smooth and cornstarch is dissolved. Set aside.
03 - Heat 1 tablespoon vegetable oil in a large wok or skillet over high heat. Add marinated beef in a single layer and sear for 1–2 minutes until browned but still slightly pink in center. Remove beef from wok and set aside.
04 - Add remaining 1 tablespoon oil to the wok. Add onions, bell peppers, garlic, and ginger. Stir-fry over high heat for 2–3 minutes until vegetables are crisp-tender and fragrant.
05 - Return the seared beef to the wok. Pour in the prepared sauce and toss to coat all ingredients. Stir-fry for 1–2 minutes until sauce thickens and coats the beef and vegetables evenly.
06 - Sprinkle with additional freshly ground black pepper to taste. Serve immediately over steamed white rice.