01 - In a bowl, combine the thinly sliced beef with 1 tablespoon soy sauce, 1 tablespoon cornstarch, and 1 teaspoon sesame oil. Mix thoroughly to coat all surfaces, then set aside to marinate for 10 to 15 minutes.
02 - In a small bowl, whisk together 3 tablespoons soy sauce, 2 tablespoons oyster sauce, 1 tablespoon rice vinegar, 2 teaspoons sugar, 2 teaspoons chili garlic sauce, 2 teaspoons cornstarch, and 4 tablespoons water until smooth. Set the sauce mixture aside.
03 - Heat 1 tablespoon of vegetable oil in a large wok or skillet over high heat until shimmering. Add the marinated beef in a single layer and stir-fry for 2 to 3 minutes, or until the beef is browned. Remove the beef from the pan and set it aside.
04 - Add the remaining 1 tablespoon of vegetable oil to the same pan. Introduce the minced garlic and grated ginger, then stir-fry for 30 seconds until their aroma becomes fragrant.
05 - Add the broccoli florets and thinly sliced red bell pepper to the pan. Stir-fry these vegetables for 2 to 3 minutes until they begin to soften slightly.
06 - Pour in 2 to 3 tablespoons of water into the pan and cover it immediately. Allow the vegetables to steam for 2 minutes, or until they are just tender-crisp.
07 - Return the browned beef to the pan with the vegetables. Pour in the prepared stir-fry sauce. Toss all ingredients together and continue to cook for 2 to 3 minutes, stirring constantly, until the sauce thickens and evenly coats the beef and vegetables.
08 - Stir in the sliced green onions. Serve the spicy beef stir-fry hot, optionally accompanied by steamed rice or noodles.