After 5 minutes very quickly add pre-fried chicken then, add white pepper powder, soy sauce, tomato ketchup, salt, and oyster sauce to the pan. Sautee the whole thing for 3 to 4 minutes. In between add the cornstarch and water mixture to the pan and mix well and turn off the flame. The sauce in the frying pan will be thick immediately. Never cook more than 5 to 10 seconds after adding cornstarch with water to any dish otherwise the dish can burn.