Start by cutting your beef chuck into 2-inch long pieces. Season the beef with soy sauce, mirin, and pepper, then let it marinate for a bit. In a separate bowl, prepare your sauce by mixing together oyster sauce, vinegar, ketchup, sugar, and chili garlic sauce. Next, throw a good amount of cornstarch onto your marinated beef and coat it thoroughly. Fry the beef in some oil until it turns golden brown. In a pan, sauté your chopped garlic, onion, and bell pepper. Once the vegetables have softened, add your mixed sauce mixture and bring it to a slight simmer. Once the sauce is simmering, add the fried beef and coat all of it with the sauce. Plate and enjoy immediately.
