In a medium-sized bowl, combine gochujang, soy sauce, honey, sesame oil, minced garlic, grated ginger, rice vinegar, and black pepper. Whisk together until smooth.

Coat chicken thighs in marinade, refrigerate for at least 1 hour.

In a large bowl, combine cabbage and carrots for slaw.

In another bowl, whisk together mayonnaise, lime juice, and sriracha (if using) for slaw dressing. Pour over cabbage and carrots, toss to coat.

Preheat grill pan over medium-high heat and lightly coat with cooking oil.

Grill marinated chicken for 6-7 minutes per side until cooked through.

Let chicken rest for 5 minutes before slicing.

Toast brioche buns until golden brown.

Assemble sandwiches with chicken, crispy slaw, cilantro, and sesame seeds.