Prepare all ingredients: slice flank steak, wash and cut broccoli, mince garlic and ginger.
Marinate the sliced beef with soy sauce, salt, and pepper for 15 minutes.
Heat 1 tablespoon of vegetable oil in a skillet over medium-high heat and stir-fry broccoli for 2-3 minutes.
In the same pan, add remaining vegetable oil and stir-fry marinated beef for 3-4 minutes until browned.
Combine soy sauce, oyster sauce, cornstarch, and beef broth in a bowl, then add to the pan with beef and broccoli, cooking for an additional 2-3 minutes until sauce thickens.
Drizzle with sesame oil and serve over rice or noodles.