Prep the chicken: Pat chicken dry, cut into bite-size pieces, then season with salt and pepper.
Coat the chicken: Toss chicken with beaten egg, then coat evenly with cornstarch.
Cook until golden: Heat oil in a large skillet. Cook chicken in a single layer for 3–4 minutes per side, until golden and cooked through.
Make the sauce: In the same skillet, cook garlic and ginger for 30 seconds. Add orange juice, zest, soy sauce, vinegar, and brown sugar. Simmer 2–3 minutes, then stir in cornstarch slurry until glossy.
Toss and serve: Return chicken to the skillet and toss with sauce. Serve immediately over rice, noodles, or vegetables.