In a mixing bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, and grated ginger. Coat the chicken thighs in this marinade, cover, and refrigerate for at least 20 minutes.

In a large bowl, combine shredded cabbage and julienned carrots. In a separate bowl, whisk together mayonnaise, rice vinegar, sugar, and a pinch of salt and pepper. Drizzle the dressing over the cabbage mixture and toss to combine. Chill for at least 15 minutes.

Heat a skillet over medium-high heat and add oil. Cook the marinated chicken thighs for 6-7 minutes on each side until golden brown and fully cooked. Let rest before slicing.

In the skillet, wipe clean and reduce heat to medium. Butter each side of the buns and toast them, butter-side down, for 2-3 minutes until crispy.

Assemble the sandwich with the toasted bun, sliced chicken, a drizzle of leftover marinade, and a generous portion of zesty cabbage slaw. Cap with the top bun and serve immediately.