In a large bowl, combine gochujang, honey, soy sauce, rice vinegar, sesame oil, minced garlic, grated ginger, and black pepper. Whisk until well combined to create the marinade.
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 your oven to 400°F (200°C).
Heat vegetable oil in a large oven-safe skillet over medium-high heat. Remove chicken from the marinade, allowing excess marinade to drip off, and place the chicken in the skillet. Sear for about 3-4 minutes on each side until golden brown.
Pour the remaining marinade over the chicken in the skillet. Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C).
Once cooked, remove the skillet from the oven and let the chicken rest for 5 minutes. Garnish with sesame seeds and sliced green onions before serving.