01 - Combine the sliced flank steak with 2 tablespoons soy sauce, Shaoxing wine, 1 teaspoon cornstarch, and 1/2 teaspoon black pepper in a bowl. Mix thoroughly to coat and let marinate for 10-15 minutes at room temperature.
02 - Whisk together 2 tablespoons soy sauce, oyster sauce, hoisin sauce, sugar, beef broth, and 1 teaspoon cornstarch in a small bowl until smooth and fully combined. 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 still slightly pink inside. Remove beef from pan and set aside on a plate.
04 - Add remaining 1 tablespoon oil to the same wok over high heat. Toss in onions, red and green bell peppers, garlic, and ginger. Stir-fry rapidly for 2-3 minutes until vegetables are crisp-tender and fragrant.
05 - Return seared beef to the wok with the vegetables. Pour in the prepared sauce and toss everything together vigorously. Continue stir-frying for 1-2 minutes until sauce thickens and coats all ingredients evenly. Season with additional black pepper to taste.
06 - Transfer the pepper steak to a serving platter immediately. Serve hot while steaming, accompanied by freshly steamed white rice for a complete meal.