Marinate the Beef: In a bowl, combine the beef slices with soy sauce, cornstarch, and rice wine. Mix well and let the beef marinate for 20–30 minutes.

Prepare the Sauce: In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, rice vinegar, sugar, water, and cornstarch. Set aside.

Stir-Fry the Vegetables: Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Add the onion, red bell pepper, and green bell pepper. Stir-fry for 2–3 minutes until they begin to soften. Remove the vegetables from the pan and set them aside.

Cook the Beef: Add the remaining 1 tablespoon of oil to the same pan. Add the marinated beef and cook for 2–3 minutes, stirring occasionally, until browned. Remove and set aside.

Combine and Serve: Return the cooked vegetables and beef to the pan. Pour the prepared sauce over the mixture and stir well to coat evenly. Cook for another 2–3 minutes until the sauce thickens and everything is heated through. Serve hot with steamed rice or noodles.