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

Combine shredded green and red cabbage with julienned carrot in a large bowl. Whisk together mayonnaise, rice vinegar, sugar, salt, and pepper in a separate bowl. Pour over the cabbage and carrot, tossing well. Chill the slaw until ready to assemble.

Heat a skillet or grill pan over medium-high heat. Cook marinated chicken thighs for about 6-7 minutes on each side until fully cooked through. Let them rest for 5 minutes before slicing.

Spread butter on cut sides of the buns and toast in the same skillet until golden brown and crispy for about 2-3 minutes on each side.

Assemble the sandwich by placing sliced chicken on the bottom half of each toasted bun. Optionally drizzle BBQ sauce, top with a scoop of cabbage slaw, and cap it with the top bun.