In a medium pot, add orange juice, sugar, vinegar, soy sauce, ginger, garlic, and red chili flakes. Heat for 3 minutes.
In a small bowl, whisk 1 tablespoon of cornstarch with 2 tablespoons of water to form a paste. Add to orange sauce and whisk together. Continue to cook for 5 minutes, until the mixture begins to thicken. Once the sauce is thickened, remove from heat and add orange zest.
Place flour and cornstarch in a shallow dish or pie plate. Add a pinch of salt. Stir.
Whisk eggs in shallow dish.
Dip chicken pieces in egg mixture and then flour mixture. Place on plate.
Heat 2–3 inches of oil in a pot over medium-high heat.
Working in batches, cook the chicken for 2–3 minutes, turning often until golden brown. Place chicken on a paper-towel-lined plate. Repeat.
Toss chicken with orange sauce. You may reserve some of the sauce to place on rice.
Serve it with a sprinkling of green onion and orange zest, if you’re fancy!