Slice the onion and bell peppers into strips or cubes. Cut the beef into cubes and marinate with a little salt and pepper for 15 minutes. Sauté the minced garlic until fragrant, then add the beef and stir-fry over high heat. Add 2 tablespoons soy sauce.

Transfer the beef to a plate. Stir-fry the vegetables until just tender, then add the beef back in and stir-fry together. Add a little oyster sauce for a glossy finish, and finally add chopped green onions.

Serve with steamed white rice. Sprinkle with ground black pepper and fried garlic if desired.