Combine chicken pieces and cornstarch into a bowl and mix until chicken is just fully coated.
Cook chicken for 7-9 minutes shaking the basket halfway through or until chicken is just at or above 165 degrees internally.
Meanwhile, combine the orange juice, brown sugar, rice wine vinegar, soy sauce, ginger, red pepper flakes, and orange zest into a small saucepan on medium heat.
Bring mixture to a simmer and simmer for 5 minutes.
Mix cornstarch and water together in a small bowl and add it to the orange sauce.
Let simmer for one additional minute while stirring then immediately remove from heat.
Remove chicken from the air fryer and combine with sauce.
Top with green onions and sesame seeds if desired and enjoy immediately!