01 - Whisk together soy sauce, oyster sauce, hoisin sauce, rice vinegar, sriracha, brown sugar, and sesame oil in a small bowl. Set aside.
02 - Mix cornstarch with water in another small bowl until smooth and well combined.
03 - Heat 1 tablespoon vegetable oil in a large skillet or wok over high heat. Add beef in a single layer and stir-fry for 2-3 minutes until browned but not fully cooked. Remove to a plate.
04 - Add remaining oil to the pan. Stir-fry garlic, ginger, broccoli, and red bell pepper for 3-4 minutes until crisp-tender.
05 - Return beef to the pan. Pour in sauce and stir to coat evenly. Cook for 1 minute.
06 - Add cornstarch slurry and stir until sauce thickens, about 1-2 minutes.
07 - Serve immediately over cooked rice, garnished with green onions.