01 - Combine sliced beef with soy sauce, oyster sauce, cornstarch, and sesame oil in a bowl. Mix thoroughly and allow to marinate for 10 minutes.
02 - Whisk together all sauce ingredients in a separate bowl until smooth. Set aside.
03 - Bring a pot of salted water to a boil. Blanch broccoli florets for 1–2 minutes until vibrant green and just tender, then drain and set aside.
04 - Heat 1 tablespoon of vegetable oil in a large wok or skillet over high heat. Stir fry the marinated beef for 2–3 minutes until browned but not fully cooked. Remove from pan and set aside.
05 - Add remaining vegetable oil to the pan. Sauté garlic, ginger, and red bell pepper (if using) for 1 minute until fragrant.
06 - Return beef and broccoli to the wok. Stir sauce and pour over ingredients. Cook while stirring for 2–3 minutes until sauce thickens and evenly coats all components.
07 - Transfer to plates and serve hot, preferably alongside steamed rice.