In a large bowl, whisk together gochujang, gochugaru, soy sauce, honey, sesame oil, minced garlic, grated ginger, and rice vinegar until well combined. Add the boneless, skinless chicken thighs, tossing to ensure each piece is thoroughly coated in the spicy marinade. Cover with plastic wrap and let it marinate in the refrigerator for at least 30 minutes, though overnight is preferred for a deeper flavor infusion.

Preheat your grill or skillet over medium-high heat. Once hot, carefully add the marinated chicken in batches, being mindful not to overcrowd the pan. Sear the chicken for about 4-5 minutes per side, checking that the internal temperature reaches 165°F (75°C) for safe consumption. The chicken should be beautifully charred and slightly caramelized before removing it from heat.

While the chicken is cooking, take a medium bowl and combine the shredded cabbage, mayonnaise, sriracha, honey, and rice vinegar. Stir the mixture until the ingredients are well-combined and creamy. Taste and adjust the spice level with extra sriracha if desired.

As the chicken finishes cooking, toast your brioche buns in a separate skillet or on the grill, cut-side down, until golden brown, which should take about 1-2 minutes.

Once the chicken is cooked and the buns are toasted, assemble your Fiery Korean Chicken Burger by layering a generous amount of slaw on the bottom bun, placing the spicy chicken thighs on top, followed by a sprinkle of sesame seeds and sliced green onions. Finally, add the top half of the bun, pressing down gently to secure your delicious creation.