To make orange sauce:

In a medium pot, add orange juice, sugar, vinegar, soy sauce, ginger, garlic, and red chilli flakes. Heat for 3 minutes.

In a small bowl, whisk 1 Tbsp of cornstarch with 2 Tbsp 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.

To make chicken:

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 heavy-bottomed pot over medium-high heat. Using a thermometer, watch for it to reach 350 degrees.

Working in batches, cook several chicken pieces at a time.Cook 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.