Orange sauce: Mix soy sauce, water, sugar, white vinegar and zest. Set aside.
Chicken: Place chicken pieces in large bowl. Stir in egg, salt, pepper and 1 tablespoon oil and mix well. Stir cornstarch and flour together. ?Pour the flour mixture over the chicken/egg mixture. Stir to coat the chicken.
?Heat oil on medium for deep-frying. ?Add chicken, small batches at a time, and fry 3 to 4 minutes or until golden crisp. (Be careful not to overcook. Remove chicken from oil with slotted spoon and drain on paper towels; set aside.
Clean wok and heat 15 seconds over high heat. Add 1 tablespoon oil. Add ginger and garlic and stir-fry until fragrant; about 10 seconds. Add and stir-fry crushed chiles and green onions. Add rice vinegar and stir 3 seconds.
Add Orange Sauce and bring to boil. Add cooked chicken, stirring until well mixed. Stir the 1/4 cup water into remaining 1 tablespoon cornstarch until smooth and add to chicken.?Heat until sauce is thickned. Stir in sesame oil and orange zest if desired.