1Preheat the air fryer to 380°F (193°C) for 5 minutes.
2Cut the chicken thighs into bite-sized pieces. Place in a bowl with the teriyaki sauce (and onion if using) and mix well. Let marinate for at least 5 minutes, up to 1 hour.
3Pour the chicken into the air fryer basket, shaking to spread it in a single layer with minimal overlapping.
4Cook for 8 minutes total, shaking the basket halfway through (after 4 minutes).
5Check for doneness by cutting into the largest piece. If still pink, cook in 1-minute increments until fully cooked.