Marinate Beef – In a bowl, toss beef with soy sauce, cornstarch, and sesame oil. Rest 10–15 minutes.
Prepare Sauce – In another bowl, whisk soy sauce, oyster sauce, vinegar, honey, ginger, garlic, broth, and cornstarch.
Cook Beef – Heat a wok/skillet over medium-high. Stir fry beef in batches until browned. Remove and set aside.
Cook Veggies – Stir fry onion, bell pepper, broccoli, carrot, and zucchini until crisp-tender (about 3–4 minutes).
Combine & Sauce – Return beef, pour in sauce, and stir. Cook 2–3 minutes until thickened.
Serve – Garnish with sesame seeds and green onions. Enjoy over rice or noodles.