In a medium bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, grated ginger, and toasted sesame seeds until smooth. Add chicken thighs to marinade and coat fully. Marinate for at least 20 minutes at room temperature or up to 2 hours in the refrigerator.

In a large bowl, mix shredded green and red cabbage with julienned carrot. In a small bowl, whisk together mayonnaise, rice vinegar, sugar, salt, and black pepper. Pour dressing over cabbage mixture and toss to coat. Refrigerate until ready to assemble the sandwich.

Preheat a cast-iron skillet or grill pan over medium-high heat, lightly oil if desired. Cook marinated chicken thighs for 6-7 minutes on each side until charred and reaching 165°F.

Remove chicken from the skillet and let it rest for 5 minutes on cutting board to redistribute juices.

Split each sandwich bun and butter each half. Toast buns on skillet over low heat or under broiler until golden brown.

Assemble sandwich with the bottom bun, grilled chicken, gochujang or BBQ sauce, and heaped cabbage slaw. Top with the other bun and enjoy.