Combine the beef, soy sauce, oyster sauce, and ground black pepper in a bowl. Mix until the beef is evenly coated.
1 lb beef sirloin, 2 tablespoons soy sauce, 1 tablespoon oyster sauce, 1/2 teaspoon ground black pepper
Add the cornstarch and toss until it evenly coats the beef. Marinate for 10 minutes.
1 1/2 tablespoons cornstarch
Heat 1 tablespoon of cooking oil in a wok or wide pan over high heat. Add the sliced bell peppers and stir-fry for 1 to 2 minutes, or until slightly tender but still crisp. Remove the bell peppers from the wok and set aside.
2 tablespoons cooking oil, 3 pieces bell peppers
Pour the remaining 1 tablespoon of cooking oil into the same wok. Once the oil is very hot, add the marinated beef and spread the slices out as much as possible. Let the beef sear for about 30 seconds before stirring.
2 tablespoons cooking oil, 1 lb beef sirloin
Stir-fry the beef for another 1 to 2 minutes, or until cooked through, sprinkling in the red pepper flakes during the last 15 to 20 seconds of cooking. Cook the beef in batches if necessary so the wok stays uncrowded.
1/4 teaspoon red pepper flakes
Return the bell peppers to the wok and add the scallions. Stir-fry for 30 to 45 seconds, or until the scallions begin to soften and the bell peppers are still crisp.
3 pieces bell peppers, 1/2 cup scallions
Transfer the Stir Fried Pepper Steak to a serving plate and serve immediately with warm rice. Share and enjoy!