In a mixing bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, grated ginger, and sesame seeds until well combined. Place the chicken thighs into the marinade, ensuring they are evenly coated. Allow to marinate for at least 20 minutes at room temperature or refrigerate for up to 2 hours.

While the chicken marinates, prepare the cabbage slaw. In a large bowl, combine shredded green and red cabbage with julienned carrot. In a separate bowl, whisk together mayonnaise, rice vinegar, sugar, salt, and pepper. Pour dressing over the cabbage mixture and toss gently. Refrigerate slaw until ready to assemble sandwiches.

Heat a skillet or grill pan over medium-high heat. Add the marinated chicken thighs and cook for 6-7 minutes on each side, or until fully cooked through (internal temperature should reach 165°F). Let the chicken rest for a few minutes before slicing.

Spread butter on each half of the buns and toast in the skillet or under a broiler until golden brown and crispy.

Assemble the sandwiches by placing a grilled chicken thigh on each toasted bun bottom. Drizzle additional BBQ sauce if desired, then top with prepared cabbage slaw. Complete with the other half of the bun.