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

Take the boneless, skinless chicken thighs and place them in a resealable plastic bag. Pour the marinade over the chicken and seal the bag tightly, then refrigerate for at least 1 hour or overnight.

In a large bowl, mix finely shredded green cabbage and julienned carrots. In a separate small bowl, whisk together mayonnaise, lime juice, and sriracha. Pour this dressing over the cabbage and carrot mixture and toss to coat. Let sit for at least 15 minutes.

Preheat a grill pan over medium-high heat. Remove the chicken from the marinade and grill each thigh for about 6-7 minutes on each side until cooked through and nice grill marks appear.

Once grilled, transfer the chicken to a cutting board and let rest for about 5 minutes before slicing into strips.

Toast the brioche burger buns on the grill pan for about 1-2 minutes until golden brown.

Assemble the sandwiches by layering the sliced grilled chicken on the toasted brioche buns and topping with the crispy slaw. Add fresh cilantro and sesame seeds, then serve immediately.