In a large bowl, combine gluten-free soy sauce, honey, rice vinegar, sesame oil, minced garlic, and grated ginger. Whisk until well blended.
Add the chicken thighs to the marinade, ensuring they are fully coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat the air fryer to 380°F (193°C).
Remove the chicken from the marinade and let excess marinade drip off. Reserve the marinade for later.
Place the chicken thighs in the air fryer basket in a single layer. Cook for 12-15 minutes, flipping halfway through, until the chicken reaches an internal temperature of 165°F (74°C).
While the chicken is cooking, pour the reserved marinade into a small saucepan. In a separate bowl, mix cornstarch and water until smooth, then add to the saucepan. Bring to a simmer over medium heat, stirring constantly until the sauce thickens.
Once the chicken is done, remove it from the air fryer and let it rest for a few minutes. Slice the chicken and drizzle with the thickened teriyaki sauce.
Garnish with sesame seeds and sliced green onions before serving.