01 - Toss beef strips with cornstarch, soy sauce, and sesame oil in a bowl. Let marinate for 10 minutes.
02 - Whisk together soy sauce, oyster sauce, chili garlic sauce, rice vinegar, brown sugar, and water in a small bowl. Set aside.
03 - Heat 1 tbsp vegetable oil in a large wok or skillet over high heat. Add beef and stir-fry for 2–3 minutes until browned but not fully cooked. Remove and set aside.
04 - Add remaining 1 tbsp oil to the pan. Stir-fry garlic, ginger, and onion for 1 minute until fragrant.
05 - Add bell peppers, carrot, snap peas, and broccoli. Stir-fry for 3–4 minutes until vegetables are crisp-tender.
06 - Return beef to the wok. Pour in sauce and stir to coat evenly. Cook 2–3 minutes until beef is cooked through and sauce thickens.
07 - Transfer to plates and serve hot, with steamed rice or noodles if desired.