In a large bowl, combine gochujang, honey, soy sauce, rice vinegar, sesame oil, minced garlic, grated ginger, and black pepper. Whisk until smooth.
Add the chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 4 hours for deeper flavor.
Preheat your air fryer to 375°F or your oven to 400°F.
If using an air fryer, arrange the marinated chicken thighs in a single layer in the basket. Cook for 18-20 minutes, flipping halfway through, until the chicken is cooked through and has a nice glaze. If baking, place the chicken on a lined baking sheet and bake for 25-30 minutes, basting with the marinade halfway through.
Once cooked, remove the chicken from the air fryer or oven and let it rest for 5 minutes.
Garnish with sesame seeds and sliced green onions before serving.