01 - Combine sliced flank steak with soy sauce, Shaoxing wine, cornstarch, and black pepper in a bowl. Mix thoroughly to coat evenly and let sit for 10-15 minutes to tenderize.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, sugar, beef broth, and cornstarch in a small bowl until cornstarch dissolves completely. Set aside for later use.
03 - Heat 1 tablespoon vegetable oil in a large wok or skillet over high heat until smoking. Add marinated beef in a single layer without overcrowding. Sear for 1-2 minutes until browned but slightly pink in center. Remove beef from pan and set aside.
04 - Add remaining tablespoon of oil to the hot wok. Toss in onions, red and green bell peppers, garlic, and ginger. Stir-fry vigorously for 2-3 minutes until vegetables are crisp-tender and fragrant.
05 - Return seared beef to the wok. Pour prepared sauce over the beef and vegetables. Toss everything together and stir-fry for 1-2 minutes until sauce thickens and coats ingredients evenly. Season with additional black pepper.
06 - Transfer pepper steak to a serving platter immediately. Serve hot while steaming, accompanied by steamed white rice for a complete meal.