01 - Whisk together soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, gochujang, rice vinegar, sesame seeds, and black pepper in a mixing bowl until the brown sugar dissolves completely.
02 - Add chicken thighs to the marinade, turning to coat all surfaces evenly. Cover and refrigerate for at least 30 minutes, up to 2 hours for deeper flavor penetration.
03 - While chicken marinates, shred carrots and purple cabbage, thinly slice cucumber and green onions, slice avocado, and cook rice if not already prepared.
04 - Combine mayonnaise, gochujang, rice vinegar, and honey in a small bowl. Whisk vigorously until completely smooth and uniformly colored. Set aside until serving.
05 - Heat a grill pan or skillet over medium-high heat. Remove chicken from marinade and grill for 5-6 minutes per side until internal temperature reaches 165°F and exterior develops charred marks. Let rest for 5 minutes before slicing.
06 - Divide warm rice evenly among four serving bowls. Arrange sliced BBQ chicken, shredded carrots, cucumber, purple cabbage, and avocado sections in quadrants over the rice.
07 - Drizzle generously with gochujang mayo, sprinkle with sliced green onions and additional sesame seeds. Serve immediately while chicken is still warm.