In a medium bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, and grated ginger. Add the chicken, coat well, and marinate for at least 20 minutes.

In a large mixing bowl, combine shredded cabbage and julienned carrot. In a separate bowl, whisk together mayonnaise, rice vinegar, sugar, salt, and black pepper. Pour dressing over cabbage mixture, toss to combine, and refrigerate for at least 15 minutes.

Heat a cast iron skillet or grill pan over medium-high heat. Lightly oil the surface. Cook marinated chicken thighs for 6-7 minutes on each side until cooked through, then let rest for 5 minutes before slicing.

Split the sandwich buns and spread butter on cut sides. Toast in a skillet until golden brown, about 2-3 minutes.

Assemble the sandwich by placing sliced chicken on the bottom half of each bun, drizzling with BBQ sauce, topping with cabbage slaw, and then placing the top bun over.