Mix the vinegar, soy sauce, ginger, garlic, and beaten egg in a sealable plastic bag. Shake to mix well. Add the chicken. Marinate for 20 mins.
Combine sauce ingredients in a saucepan over medium heat. Stir well and simmer for 5 mins to thicken slightly.
In another sealable plastic bag, mix the flour, cornstarch, and baking powder.
Remove the chicken from the marinade, shaking off any excess. Transfer the chicken to the flour bag. Shake to coat the chicken. Place it on a wire rack for 5 minutes to soak up the flour.
Spray the chicken with cooking oil, then place it in the air fryer basket, not touching.
Air fry at 400ºF (205ºC) for 6 mins. Carefully turn the chicken over, spray again, and cook for another 4-5 mins, until the internal temperature reaches 165ºF (75°C).
Transfer the chicken to a bowl. Pour on sauce and toss to coat. Serve with sesame seeds and green onions.