In a large bowl, whisk together the cornstarch, flour, salt, and pepper. In a separate bowl, beat the eggs. Dip each chicken piece into the egg, then dredge in the flour mixture until well-coated. Place coated chicken on a plate.

Pour the vegetable oil into a large frying pan or wok and heat over medium-high until shimmering. Fry the chicken pieces in batches for 4-5 minutes, turning occasionally, until golden and cooked through. Remove with a slotted spoon and drain on paper towels.

In a small saucepan, combine the orange juice, soy sauce, rice vinegar, sugar, orange zest, ginger, garlic, and chili flakes. Bring to a gentle simmer over medium heat.

In a small bowl, mix the cornstarch and water to make a slurry, then stir into the sauce. Continue simmering for 2-3 minutes, stirring, until thickened and glossy.

Place the fried chicken in a large clean bowl, pour the hot orange sauce over the chicken, and toss gently to coat all the pieces.

Plate the orange chicken and sprinkle with green onions and sesame seeds. Serve immediately with steamed white rice or fried rice.