In a large bowl, whisk together pineapple juice, soy sauce, brown sugar, olive oil, garlic, ginger, black pepper, and red pepper flakes. This will be your marinade.
Place the pork chops in the marinade, ensuring they are fully submerged. Cover and refrigerate for at least 1 hour, or up to 4 hours for more flavor.
Preheat your grill to medium-high heat. Remove the pork chops from the marinade and let excess marinade drip off. Discard the marinade.
Grill the pork chops for about 6-8 minutes on each side, or until they reach an internal temperature of 145°F. During the last few minutes of grilling, add the fresh pineapple slices to the grill and cook until caramelized, about 2-3 minutes per side.
Once cooked, remove the pork chops and pineapple from the grill. Let the pork chops rest for 5 minutes before serving.
Serve the pork chops topped with grilled pineapple and garnished with chopped green onions.