Slice beef into thin slices with the grain. Cut each strip across the grain about 1" long so you have small thin slices. Place in a bowl and add 4 teaspoon of soy sauce, 1 tablespoon of rice wine, 1 teaspoon cornstarch and black pepper.

In a small bowl, mix 3 tablespoon soy sauce, 1 tablespoon water and 2 teaspoon cornstarch. Set aside.

Heat the wok on high heat. Swirl in 2 teaspoons of the oil and add the beef spreading evenly in the wok. Cook undisturbed for 20 seconds letting the beef brown. Using a spatula, stir meat, cooking another 2 minutes. Transfer to a plate.

Add remaining teaspoon of oil to wok, add peppers and onions and cook about 4 to 5 minutes. Return beef to the wok, add the sauce and red pepper flakes and stir fry about 30 seconds until slightly thickened.