1. Prepare the marinade by mixing pineapple juice, soy sauce, brown sugar, ketchup, minced garlic, grated ginger, sriracha, and lemon juice in a bowl.
2. Place the boneless, skinless chicken thighs in a resealable bag or shallow dish and pour the marinade over them.
3. Cover and refrigerate for at least 4 hours or overnight for best flavor.
4. Preheat the grill, stovetop pan, oven, or slow cooker depending on your cooking method preference.
5. Remove the chicken from the marinade, letting the excess drip off, and reserve the marinade for basting.
6. Cook the chicken thighs on a preheated grill over medium heat for 5-7 minutes per side until fully cooked and slightly charred.
7. Baste the chicken with the reserved marinade while cooking to enhance flavor and moisture.
8. If using the stovetop, cook in a heated pan over medium-high heat, flipping occasionally until fully cooked.
9. If using the oven, bake at 375°F (190°C) for 25-30 minutes, basting occasionally.
10. If using a slow cooker, cook on low for 6-7 hours or on high for 3-4 hours.
11. Grill pineapple slices for a few minutes on each side until caramelized and slightly charred.
12. Serve the Hawaiian chicken thighs with grilled pineapple slices and a side of rice.
13. Garnish with sliced green onions and sesame seeds for added flavor and presentation.
14. Enjoy as part of a Hawaiian plate lunch with rice and macaroni salad if desired.