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

Place the boneless, skinless chicken thighs into a resealable bag or a shallow bowl. Pour the prepared marinade over the chicken and refrigerate for at least 1 hour, ideally overnight.

In a large bowl, mix the shredded green cabbage and julienned carrots. In a separate small bowl, whisk together mayonnaise, lime juice, and sriracha until smooth. Pour dressing over the cabbage and carrots, tossing to coat.

Preheat your grill pan over medium-high heat. Lightly oil the pan, add the marinated chicken thighs, and grill for 6–7 minutes on each side until cooked through.

Transfer the grilled chicken to a cutting board to rest for 5 minutes before slicing.

Grill or toast the brioche buns until golden brown, about 2–3 minutes per side.

To assemble, layer the sliced grilled chicken on the bottom bun, top with the crispy slaw, garnish with cilantro and sesame seeds, and cover with the top bun. Serve immediately.