01 - Whisk together soy sauce, pineapple juice, brown sugar, ketchup, rice vinegar, ginger, garlic, sesame oil, honey, smoked paprika, and pepper in a large bowl until thoroughly combined.
02 - Measure out 1/2 cup of the marinade and set aside separately for basting during grilling.
03 - Place chicken pieces in a large resealable bag or shallow dish. Pour remaining marinade over the chicken, coating all pieces completely. Cover and refrigerate for at least 2 hours, preferably overnight.
04 - Heat grill to medium-high, approximately 400°F. Lightly oil the grates to prevent sticking.
05 - Remove chicken from marinade and discard used liquid. Pat chicken pieces dry with paper towels.
06 - Place chicken skin-side down on the grill. Cook for 6-8 minutes until nicely seared, then flip and grill for an additional 6-8 minutes.
07 - Brush chicken with reserved marinade. Continue grilling, turning and basting every 2-3 minutes, until cooked through and caramelized. Internal temperature should reach 165°F, approximately 20-25 minutes total grilling time.
08 - Transfer chicken to a platter and let rest for 5 minutes. Sprinkle with scallions, sesame seeds, and diced pineapple if desired. Serve hot.