01 - Combine beef slices with soy sauce, cornstarch, and sesame oil in a bowl. Toss thoroughly to coat and let marinate for 10-15 minutes at room temperature.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, rice vinegar, sriracha, brown sugar, and water in a separate bowl until smooth and well combined. Set aside.
03 - Heat 1 tbsp vegetable oil in a large wok or skillet over high heat until smoking. Add marinated beef in a single layer and sear for 1-2 minutes per side until just browned. Remove beef to a plate and set aside.
04 - Add remaining 1 tbsp oil to the wok. Stir fry garlic and ginger for 30 seconds until fragrant, being careful not to burn them.
05 - Add broccoli and bell pepper to the wok. Stir fry for 2-3 minutes. Pour in 2 tbsp water, cover, and steam for 2 minutes until broccoli is tender-crisp.
06 - Return beef to the wok. Pour in prepared sauce and toss everything together. Stir fry for 2-3 minutes until sauce thickens and evenly coats all ingredients.
07 - Remove from heat immediately. Garnish with sliced green onions and toasted sesame seeds. Serve hot with steamed rice or noodles.