In a large skillet over medium heat, cook the ground beef until browned and fully cooked. Drain excess fat if needed, and set aside.
Add a splash of water to the skillet and toss in the broccoli florets. Cover and steam for 3–4 minutes until tender-crisp. Remove lid and cook off any excess water.
In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, cornstarch, water, garlic, ginger, and rice vinegar.
Return the cooked ground beef to the skillet with the broccoli. Pour in the sauce and stir to coat everything evenly. Simmer for 2–3 minutes until the sauce thickens and clings to the meat and broccoli.
Serve hot over rice or noodles. Garnish with sesame seeds and sliced green onions if desired.