Slice the beef thin: Freeze the steak for 15–20 minutes to firm it up, then slice thinly against the grain. Pat dry with paper towels.
Make the sauce: In a bowl, whisk soy sauce, broth, rice vinegar, sesame oil, brown sugar or honey, and cornstarch.
Add red pepper flakes if you like heat.
Steam-blanch the broccoli: Microwave or steam broccoli for 2–3 minutes until bright green and crisp-tender. Set aside.
Heat the pan: Set a large skillet or wok over medium-high heat. Add half the oil.
Sear the beef: Add half the beef in a single layer.
Cook 60–90 seconds per side until just browned. Remove to a plate. Repeat with remaining oil and beef.
Sauté aromatics: Add garlic and ginger to the empty pan.
Stir 20–30 seconds until fragrant, being careful not to burn.
Combine: Return beef and broccoli to the pan. Pour in the sauce. Toss and cook 1–2 minutes until the sauce thickens and coats everything.
Taste and adjust: Add a splash of broth for a lighter sauce or a pinch of sugar/honey if you want more balance.
Season with pepper.
Serve: Top with green onions and sesame seeds. Serve over cauliflower rice for a lower-calorie option or a small scoop of brown rice.