Gather ingredients: chicken (boneless, bite-size), cornstarch, salt, black pepper, eggs, orange juice, orange zest (optional), soy sauce, rice vinegar (or distilled vinegar), brown sugar (or honey), garlic (minced), ginger (grated), ketchup (optional), chili flakes (optional), vegetable oil
Make the sauce: whisk orange juice, soy sauce, vinegar, brown sugar, ketchup (if using), garlic, ginger, and chili flakes in a bowl until smooth
Coat chicken: season chicken with salt and black pepper
Set up coating: beat eggs in one bowl; place cornstarch in another bowl
Coat chicken: dip chicken in egg, then coat thoroughly in cornstarch
Fry chicken: heat vegetable oil to 350°F (175°C); fry chicken in batches until golden and crisp, 3–5 minutes
Drain: transfer fried chicken to a rack or paper towels to drain
Thicken sauce: pour sauce into a saucepan and bring to a simmer; cook 2–4 minutes until slightly reduced
Gloss the chicken: add fried chicken to the saucepan or toss with sauce in a bowl
Serve: top with orange zest (optional) and serve immediately with rice or vegetables