Marinate the chicken:
In a mixing bowl, whisk together pineapple juice, brown sugar, soy sauce, olive oil, chili flakes, minced garlic, ground ginger, paprika, salt, and pepper.
Place the chicken in a ziplock bag or shallow dish and pour the marinade over it. Seal the bag (or cover the dish) and refrigerate for at least 30 minutes (or up to 2 hours for a stronger flavor).
Preheat:
If grilling or baking, preheat the grill to medium heat or the oven to 375°F (190°C).
Cook the chicken:
Grill: Remove the chicken from the marinade and place it on the grill. Grill each side for 5-7 minutes or until fully cooked (internal temperature reaches 165°F/74°C). Baste occasionally with the marinade for extra flavor.
Pan-fry: Heat a skillet over medium-high heat with a little oil. Sear the chicken for 6-7 minutes per side until browned and cooked through.
Bake: If baking, transfer the chicken to a baking dish and pour some of the remaining marinade over it. Bake for 25-30 minutes, basting halfway through.
Add pineapple chunks:
In the last 5 minutes of cooking, add the pineapple chunks to the grill, pan, or baking sheet to caramelize slightly, or heat them separately in a skillet for a few minutes until golden.
Optional jalapeño: If you want more heat, grill or sauté the jalapeño slices along with the chicken and pineapple.
Serve:
Once cooked, remove the chicken from the heat. Let it rest for a couple of minutes before slicing.
Garnish with fresh cilantro or parsley if desired and serve with the caramelized pineapple chunks on the side or on top.