01 - Combine the beef with 2 tbsp soy sauce, cornstarch, and sesame oil in a medium bowl. Toss to coat evenly and let marinate for 10 minutes at room temperature.
02 - Whisk together 3 tbsp soy sauce, oyster sauce, hoisin sauce, chili garlic sauce, rice vinegar, brown sugar, and water in a small bowl until sugar dissolves. Set aside.
03 - Heat 1 tbsp vegetable oil in a large skillet or wok over high heat. Add marinated beef in a single layer and sear for 1-2 minutes per side until browned but not fully cooked through. Remove beef from pan and set aside.
04 - Add remaining 1 tbsp oil to the hot pan. Stir fry minced garlic and grated ginger for 30 seconds until fragrant, being careful not to burn.
05 - Add broccoli florets and sliced red bell pepper to the pan. Stir fry for 2-3 minutes until vegetables are tender-crisp.
06 - Return seared beef and green onions to the pan. Pour in the prepared sauce and stir well to coat everything. Cook for 2-3 minutes until sauce thickens and beef is cooked through.
07 - Remove from heat. Sprinkle with toasted sesame seeds and fresh cilantro. Serve immediately with steamed rice or noodles.