Prep the marinade: In a large resealable bag, mix brown sugar, ketchup, canned pineapple juice, soy sauce, Worcestershire sauce, apple cider vinegar, ginger, garlic, smoked paprika, and ground black pepper until evenly combined.
Reserve ½ cup of the marinade and store in the fridge for later. It will be used to baste the chicken.
Marinate the chicken: Add the chicken thighs into the marinade in the resealable bag, making sure it’s all coated evenly. Seal the bag and marinate in the fridge for at least 4-6 hours or preferably overnight.
Before grilling: Remove the marinated chicken from the fridge and let it sit on the counter for about 20-30 minutes. Meanwhile, get a grill pre-heated and brush the grill grates with oil.
Cook the chicken: Grill chicken for 6 minutes on one side, then flip and cook for about 3 minutes. Baste the chicken with the reserved ½ cup of the marinade, then flip again and cook for another 1-2 minutes on each side at a time. Repeat until fully cooked through in the center. They should cook for about 15-16 minutes total, depending on the size (use a thermometer to be sure). Remove from grill and let it rest for 10 minutes. Note: Avoid cross-contamination by only use the reserved marinade to brush the chicken.
Grill the pineapple slices on both sides until you get beautiful grill marks. Tip: Let them grill undisturbed per side, once they develop grill marks, they should release easily.
Serve the huli huli chicken with the grilled pineapple and garnish with green onions. Enjoy!