In a mixing bowl, combine the orange juice, sugar, vinegar, soy sauce, ginger, garlic, and red chili flakes. Whisk until the sugar is dissolved.
In a small bowl, mix the cornstarch with cold water until smooth. Add this mixture to the sauce and whisk to combine. Set aside.
Cut the chicken into bite-sized pieces. Beat the eggs in a separate bowl. Mix cornstarch and flour in another bowl. Dip chicken in egg, then dredge in cornstarch and flour mixture.
In a deep skillet, heat about 2 inches of oil over medium-high heat. Once hot, add coated chicken pieces in batches and fry for 4-5 minutes until golden brown. Remove with a slotted spoon and drain on paper towels.
In the same skillet, drain excess oil, leaving about 1 tablespoon. Pour in the prepared sauce and bring to a simmer, stirring frequently until thickened, about 3-5 minutes.
Once the sauce thickens, add the fried chicken and toss to coat evenly. Add the orange zest and mix well.
Serve hot, garnished with green onions and additional orange zest. Pair with steamed rice or stir-fried vegetables.