In a medium bowl, whisk together brown sugar, soy sauce, water, minced garlic, gochujang, rice vinegar, sesame oil, ginger, green onions, sesame seeds, and black pepper until sugar is dissolved.

Reserve about 1/3 of the marinade for basting during grilling.

Place your chicken in a large zip-top bag or shallow dish and pour the remaining marinade over it. Seal and refrigerate for at least 30 minutes, but preferably 4-8 hours for maximum flavor penetration.

Preheat your grill to medium-high heat (around 375-400°F). If using a charcoal grill, prepare for indirect heat cooking.

Remove chicken from the marinade, allowing excess to drip off. Discard the used marinade.

Grill chicken for 5-7 minutes per side (for boneless pieces) or until the internal temperature reaches 165°F. Brush with the reserved marinade during the last few minutes of cooking for a glossy, caramelized finish.

Transfer to a clean plate and let rest for 5 minutes before serving.

Garnish with additional sliced green onions and sesame seeds for an authentic presentation.