In a bowl, combine soy sauce, honey or maple syrup, rice vinegar, sesame oil, garlic, and ginger.
Add the chicken to the marinade, making sure they are well coated. Let it marinate for at least 10 minutes.
Preheat the air fryer to 400°F (200°C). Lightly spray the air fryer basket with cooking oil.
Place the marinated chicken in the basket in a single layer.
Air fry for 18-20 minutes, flipping the chicken halfway through to ensure even cooking.
While the chicken is cooking, pour the remaining marinade into a small saucepan and bring it to a simmer over medium heat. Continue boiling for at least 5 minutes.
If the sauce becomes too thick, add a small amount of water and whisk well.
If a thicker sauce is desired, mix the cornstarch with water to make a slurry. Slowly whisk the slurry into the simmering sauce, stirring constantly until the sauce thickens, about 1-2 minutes.
Once the chicken is cooked, toss it in the thickened teriyaki sauce until well coated.
Transfer the chicken to a serving dish and garnish with sesame seeds and chopped green onions if desired.