Whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, and grated ginger in a medium bowl. Coat chicken thighs in the marinade, cover, and refrigerate for at least 20 minutes.

In a large bowl, combine shredded green and red cabbage with julienned carrot. In a small bowl, whisk together mayonnaise, rice vinegar, sugar, salt, and pepper. Pour dressing over cabbage mixture and toss to coat. Chill.

Heat a skillet or grill pan over medium-high heat. Cook marinated chicken thighs for 6-7 minutes on each side until caramelized and internal temperature reaches 165°F. Let rest before slicing.

Butter the cut sides of the buns and toast them cut-side down in the skillet for 2-3 minutes until golden brown.

Assemble the sandwich with sliced chicken on the bottom bun, layer with slaw, and top with sesame seeds. Serve immediately.