Cut the beef into thin strips. Place in a bowl and add 4 tsp of soy sauce,1tsp cornstarch and black pepper.

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

Heat the wok on high heat. Swirl in 1 tblsp 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 1 tblsp 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,salt according to your taste and stir fry about 30 seconds until slightly thinkend served with boiled rice.