In a large bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, minced garlic, and freshly grated ginger until well combined. Add the boneless, skinless chicken thighs, ensuring they are fully coated in the marinade. Cover the bowl with plastic wrap and let it marinate at room temperature for 20 minutes or up to 2 hours in the refrigerator for deeper flavor.

In a large mixing bowl, combine shredded green and red cabbage and julienned carrots. In a separate small bowl, whisk together mayonnaise, rice vinegar, sugar, salt, and pepper until smooth. Drizzle this creamy mixture over the cabbage and carrot blend, tossing everything together until well combined. Chill the slaw in the refrigerator for at least 15 minutes to enhance the flavors.

Heat a non-stick skillet or grill pan over medium-high heat. Remove the marinated chicken thighs from the bowl, allowing excess marinade to drip off. Place the chicken in the hot skillet and cook for about 6-7 minutes per side, or until the internal temperature reaches 165°F (74°C) and the chicken is nicely caramelized. Once cooked, transfer the chicken to a cutting board and let it rest for a few minutes before slicing.

Spread butter evenly on the cut sides of each bun. In a separate non-stick skillet over medium heat, place the buns butter-side down and toast them until golden brown, approximately 2-3 minutes.

Start by placing the sliced chicken on the bottom half of each toasted bun. Drizzle some reserved marinade over the chicken for extra flavor if desired. Generously top the chicken with the chilled cabbage slaw before placing the top bun on it.