In a mixing bowl, whisk together soy sauce, brown sugar, honey, gochujang, rice vinegar, sesame oil, garlic, and fresh ginger until blended. Add the boneless skinless chicken thighs, ensuring they are well-coated in the marinade. Cover the bowl with plastic wrap and let it marinate for at least 20 minutes at room temperature, or refrigerate for up to 2 hours for deeper flavor infusion.

While the chicken marinates, grab a large bowl and mix together the shredded green and red cabbage with the julienned carrot. In a separate small bowl, whisk together mayonnaise, sugar, and a dash of rice vinegar. Combine the dressing with the cabbage mixture, tossing everything until evenly coated, then cover and chill in the refrigerator for at least 15 minutes to let the flavors meld.

Preheat your grill or grill pan to medium-high heat. Remove the chicken thighs from the marinade, letting any excess drip off. Grill the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F (74°C) and the meat has nice grill marks. Once cooked, transfer the chicken to a plate and let it rest for a few minutes before slicing.

As the chicken rests, take your brioche or potato sandwich buns and spread butter on the cut sides. Heat a skillet over medium heat, then place the buns cut-side down, toasting them for about 2-3 minutes or until they're golden brown and crispy.

Now that everything is ready, it's time to build your Korean BBQ Chicken Sandwich. Start by placing a generous layer of sliced grilled chicken on the bottom half of each toasted bun. Top it with a hearty scoop of the zesty cabbage slaw for a refreshing crunch. Finally, place the top bun on and press down gently to secure all those delicious flavors in place.