In a large shallow bowl, whisk together 1 cup cornstarch, 1/4 cup flour, 1/2 teaspoon salt, and 1/4 teaspoon black pepper.
Place the beaten eggs in a separate bowl.
Heat about 2 inches of canola oil in a deep frying pan over medium-high until it reaches 325–350°F (use a thermometer).
Dip the chicken pieces into the beaten eggs, then toss them in the cornstarch-flour mixture to coat; work in batches so pieces are evenly coated.
Fry the coated chicken in batches in the hot oil until golden and crispy, then transfer to a paper-towel-lined plate to drain.
Wipe out the pan and add orange juice, white sugar, brown sugar, rice vinegar, soy sauce, minced ginger, minced garlic, and red pepper flakes; bring to a simmer over medium heat and cook about 3 minutes.
In a small bowl, whisk 1 tablespoon cornstarch with 2 tablespoons water to make a slurry, then whisk it into the simmering sauce and cook 3–5 minutes until thickened.
Reduce heat to low and stir in the orange zest, then add the fried chicken back to the pan and toss to coat thoroughly in the sauce.
Serve the orange chicken over white rice and sprinkle with chopped green onions and additional orange zest if desired.
