Combine soy sauce, oyster sauce, hoisin sauce, brown sugar, and beef broth in a bowl. Set aside.
Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Add beef slices and cook until browned, about 3-4 minutes. Remove the beef and set aside.
In the same pan, add the remaining oil, garlic, and ginger. Sauté for 30 seconds until fragrant.
Add broccoli florets and stir-fry for 3-4 minutes until crisp-tender.
Return the beef to the pan. Pour the sauce mixture over it and stir to coat.
Add the cornstarch slurry, stirring constantly until the sauce thickens, about 1-2 minutes.
Serve hot over steamed rice or noodles. Garnish with sesame seeds and green onions if desired.
