Prepare Marinade: In a mixing bowl, combine gochujang, soy sauce, honey, sesame oil, minced garlic, grated ginger, rice vinegar, and black pepper. Whisk until smooth.

Marinate Chicken: Coat chicken thighs in marinade, seal in a bag or bowl, refrigerate for at least 1 hour or overnight for best flavor.

Make Slaw: Mix cabbage and carrots in a bowl. In a separate bowl, whisk mayo, lime juice, and sriracha. Toss with cabbage and carrots.

Grill Chicken: Preheat grill pan over medium-high heat. Lightly oil and grill chicken for 6-7 minutes per side until cooked through.

Rest and Slice: Let grilled chicken rest for a few minutes, then slice into strips for the sandwich.

Toast Buns: Lightly toast brioche buns on the grill or in a toaster until golden brown.

Assemble Sandwiches: Layer sliced chicken on the bottom half of each bun, top with slaw, cilantro, and sesame seeds, and finish with the top bun.