Heat the vegetable oil in a large skillet or wok over medium-high heat.
Add the diced onion and stir-fry for about 2 minutes until translucent.
Stir in the minced garlic and ginger, cooking for an additional minute.
Add the ground beef to the skillet. Cook until it is browned and no longer pink, breaking it apart with a spatula (about 5-7 minutes).
While the beef is cooking, steam the broccoli in a separate pot or microwave until just tender (about 3-4 minutes).
Once the beef is cooked, add the soy sauce, oyster sauce (if using), sesame oil, and sugar. Stir well to combine.
Add the steamed broccoli to the skillet, tossing everything together for about 2-3 minutes until well mixed and heated through.
Season with salt and pepper to taste.
Serve hot over cooked rice or noodles.