In a large bowl, combine gochujang, soy sauce, honey, sesame oil, minced garlic, ground ginger, and black pepper. Mix well to create a marinade.
Add the chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat the air fryer to 400°F (200°C).
Remove the chicken from the marinade and shake off any excess. Place the chicken thighs skin-side down in the air fryer basket in a single layer.
Cook for 15 minutes, then flip the chicken thighs and cook for an additional 10-15 minutes, or until the internal temperature reaches 165°F (74°C) and the skin is crispy.
Remove the chicken from the air fryer and let it rest for 5 minutes. Garnish with sesame seeds and sliced green onions before serving.