Mix brown sugar, ketchup, pineapple juice, soy sauce, Worcestershire sauce, apple cider vinegar, ginger, garlic, paprika, and black pepper in a resealable bag.
Reserve ½ cup of marinade in the fridge for basting.
Add chicken thighs to the marinade, coat evenly, seal, and refrigerate for 4-6 hours or overnight.
Let chicken sit at room temperature for 20-30 minutes. Preheat and oil the grill.
Grill chicken for 6 minutes on one side, flip, cook for 3 minutes, baste with reserved marinade, flip, and cook for another 1-2 minutes per side, about 15-16 minutes total. Rest for 10 minutes.
Grill pineapple slices until marked.
Serve chicken with grilled pineapple and garnish with green onions. Enjoy!