Make the sauce: In a small saucepan, whisk together the orange juice, orange zest, brown sugar, soy sauce, rice vinegar, garlic, ginger, and red pepper flakes. Bring to a simmer over medium heat.

Thicken the sauce: Stir the 1 tablespoon cornstarch and 2 tablespoons water together into a slurry, then whisk it into the simmering sauce. Cook for 1 to 2 minutes until glossy and thick enough to coat a spoon. Remove from the heat and set aside.

Coat the chicken: Season the chicken with the salt and pepper. Beat the egg in one bowl and put the 1/2 cup cornstarch in another. Dip each piece in the egg, then toss in the cornstarch until fully coated, shaking off the excess.

Preheat and spray: Preheat the air fryer to 400°F. Arrange the chicken in a single layer with space between the pieces and spray well with olive oil, covering any dry cornstarch spots.

Air fry: Air fry at 400°F for 10 to 12 minutes, shaking the basket and spritzing again with oil halfway through, until golden, crisp, and cooked to 165°F inside. Work in batches so the pieces aren't crowded. Air fryers vary, so use the internal temp as the real test.

Toss and serve: Add the hot, crispy chicken to the warm orange sauce and toss just to coat, right before serving. Garnish with sesame seeds and green onion and serve over rice.