In a bowl, mix beef with soy sauce, oyster sauce, sesame oil, black pepper, and cornstarch. Let marinate for 15 minutes.
Heat vegetable oil in a wok over high heat. Add marinated beef and stir-fry until browned. Remove from the wok and set aside.
In the same wok, sauté bell pepper, onion, and garlic until fragrant.
Return beef to the wok, pour in beef broth and sugar, and stir-fry for another 2 minutes until sauce thickens.
Serve hot with steamed rice or noodles.