In a bowl, combine sliced steak with 1 tablespoon soy sauce and 1 tablespoon cornstarch. Mix well and let it marinate for 15–20 minutes. This helps tenderize the meat and locks in flavor while cooking.

Heat 1 tablespoon oil in a hot skillet or wok. Add the beef in a single layer and sear quickly for 2–3 minutes until browned but not fully cooked. Remove from the pan and set aside. Cooking in batches prevents steaming and keeps the meat tender.

In the same pan, add remaining oil along with garlic and ginger. Sauté briefly until fragrant, then toss in sliced onions and bell peppers. Stir-fry for 2–3 minutes until slightly tender but still crisp.

Return the beef to the pan. Add remaining soy sauce, oyster sauce, beef broth, sugar, black pepper, sesame oil, and remaining cornstarch (mixed with a little water). Stir well and cook for 2–3 minutes until the sauce thickens and coats everything evenly. Serve hot.