Marinate the Chicken: In a mixing bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, ginger, and sesame seeds until smooth. Coat the chicken thighs evenly with this marinade. Let it marinate for 20 minutes at room temperature or refrigerate for up to 2 hours.

Prepare Cabbage Slaw: In a large bowl, combine shredded cabbage and julienned carrot. In a separate bowl, whisk together mayonnaise, rice vinegar, a pinch of sugar, salt, and pepper. Toss dressing with cabbage mixture to coat and chill in the refrigerator.

Cook the Chicken: Heat a large skillet over medium-high heat. Cook marinated chicken thighs for 6-7 minutes on each side until fully cooked with an internal temperature of 165°F (75°C). Let rest for 5 minutes.

Toast the Buns: Melt butter in a skillet over medium heat. Cut buns in half, butter the cut sides, and toast in the skillet until golden.

Assemble the Sandwich: Place the toasted bottom bun on a plate. Add chicken slices, heap with slaw, and top with the bun. Serve immediately.