In a large bowl, combine the sweet chili sauce, soy sauce, olive oil, garlic powder, onion powder, black pepper, salt, and red pepper flakes (if using). Mix well to create a marinade.
Add the chicken thighs to the marinade, ensuring they are fully coated. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat the air fryer to 380°F.
Remove the chicken thighs from the marinade, allowing excess marinade to drip off. Place the chicken thighs in a single layer in the air fryer basket, skin side up.
Cook the chicken thighs in the air fryer for 25-30 minutes, or until the internal temperature reaches 165°F and the skin is crispy. Flip the thighs halfway through cooking for even crispiness.
Once cooked, let the chicken rest for 5 minutes before serving. Garnish with chopped green onions.