In a bowl, combine cornstarch, flour, salt, and pepper. In a separate bowl, beat the egg.
Dip chicken pieces in the egg, then dredge in the flour mixture.
Heat oil in a pan over medium-high heat. Fry chicken until golden and cooked through. Set aside.
In a clean pan, heat a little oil and sauté garlic, ginger, and red chili flakes for 30 seconds.
Add soy sauce, water, orange juice, orange zest, sugar, and vinegar. Bring to a boil.
Mix cornstarch with water to make a slurry and stir into the sauce. Cook until thickened.
Add fried chicken to the sauce and toss until well coated. Serve hot.