Prepare two bowls; one with beaten egg, another with the flour. Dip chicken in egg mixture, coat in flour, set aside. Fry chicken until completely cooked.
In a large saucepan combine 1 ½ cups water, orange juice, rice vinegar, and soy sauce. Stir over medium heat until thoroughly combined. Stir in brown sugar, orange zest, ginger, garlic and red pepper. Bring mixture to a boil. Taste sauce and add more brown sugar and zest if needed.
Combine 3 tablespoons of cornstarch with ¼ cup of water and mix thoroughly. Slowly stir cornstarch mixture into sauce until it thickens. Pour sauce over fried chicken. Assemble sandwich, garnishing chicken with cole slaw and green onions.
Recipe by at http://sophistishe.com/2014/01/orange-chicken-sandwich/