Make the sauce: In a small bowl, whisk soy sauce, broth, brown sugar or honey, rice vinegar, oyster sauce, chili-garlic sauce (if using), cornstarch, and sesame oil until smooth.
Set aside.
Prep the veggies: Cut broccoli into small, even florets. Thinly slice the onion. Mince the garlic and ginger.
Keep everything close to the stove so it’s ready to go.
Blanch or steam the broccoli (quick method): To keep it crisp-tender, microwave broccoli with a splash of water for 1–2 minutes, or blanch in boiling water for 1 minute and drain well. This step helps it cook fast in the skillet.
Brown the beef: Heat 1 tablespoon oil in a large skillet over medium-high heat. Add the ground beef and break it up.
Season lightly with salt and pepper. Cook until browned and most liquid evaporates, about 5–7 minutes. Transfer to a plate and drain excess fat if needed, leaving a thin layer in the pan.
Cook aromatics and onion: Add remaining 1 tablespoon oil to the skillet.
Add onion and cook 2–3 minutes until slightly softened. Stir in garlic and ginger and cook 30–45 seconds until fragrant. Don’t let it burn.
Stir-fry the broccoli: Add broccoli to the skillet and toss for 1–2 minutes to heat through and pick up flavor.
Combine and sauce: Return the beef to the skillet.
Whisk the sauce again (cornstarch sinks) and pour it over everything. Toss and cook 1–2 minutes until the sauce thickens and coats the beef and broccoli.
Taste and adjust: Add a splash more soy for salt, a pinch of sugar for balance, or extra chili sauce for heat. Remove from heat.
Garnish and serve: Sprinkle with green onions and sesame seeds if you like.
Serve hot over rice or noodles.