Make the sauce: In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, sesame oil, cornstarch, beef broth, brown sugar, and red pepper flakes. Set aside.
Cook the ground beef: Heat olive oil in a large skillet or wok over medium-high heat. Add ground beef and cook until browned, breaking it apart with a spatula. Drain excess grease if necessary.
Add garlic and ginger: Stir in minced garlic and grated ginger, cooking for 1 minute until fragrant.
Cook the broccoli: Add broccoli florets to the pan and stir-fry for 3-4 minutes until tender-crisp.
Add the sauce: Pour the sauce over the beef and broccoli mixture, stirring well to coat everything. Let it simmer for 2-3 minutes until the sauce thickens.
Garnish and serve: Sprinkle with chopped green onions and sesame seeds. Serve hot over rice or noodles!