In a bowl, mix the sliced beef with soy sauce and cornstarch. Let it marinate for 10 minutes.
Heat vegetable oil in a large pan or wok over medium-high heat.
Add the beef and cook for 2-3 minutes until browned. Remove from the pan and set aside.
In the same pan, add the onions and garlic. Sauté for 2 minutes until fragrant.
Stir in oyster sauce, hoisin sauce, black pepper, sugar, and beef broth.
Return the beef to the pan and stir-fry for another 2 minutes until well coated.
Garnish with green onions and sesame seeds. Serve hot with rice or noodles.