In a large bowl, combine soy sauce, honey, gochujang, rice vinegar, minced garlic, grated ginger, sesame oil, and black pepper. Whisk until well blended 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.
Heat vegetable oil in a large skillet over medium-high heat. Remove chicken from the marinade (reserve the marinade) and add to the skillet. Sear the chicken for about 5 minutes on each side, until browned.
Pour the reserved marinade over the chicken in the skillet. Bring to a simmer, then reduce the heat to low. Cover and cook for 20-25 minutes, or until the chicken is cooked through and tender.
Remove the lid and let the sauce reduce for an additional 5 minutes, stirring occasionally.
Serve the chicken hot, garnished with sliced green onions and sesame seeds.