In a bowl, mix together pineapple juice, soy sauce, garlic, brown sugar, ginger, salt, and pepper to create the marinade.
Place the pork tenderloin in a large resealable plastic bag or a shallow dish, and pour the marinade over it. Seal the bag or cover the dish, and marinate in the refrigerator for at least 2 hours, preferably overnight.
Preheat your oven to 375°F (190°C).
Heat a large oven-safe skillet over medium-high heat. Remove the pork from the marinade (reserve the marinade) and sear it on all sides until browned, about 2-3 minutes per side.
Pour the reserved marinade over the pork in the skillet.
Transfer the skillet to the preheated oven and cook for about 25-30 minutes, or until the internal temperature of the pork reaches 145°F (63°C).
While the pork is cooking, you can grill the pineapple rings on a grill pan or skillet for a couple of minutes on each side.
Once the pork is done, remove it from the oven and let it rest for a few minutes before slicing.
Serve the sliced pork topped with the grilled pineapple rings and garnish with chopped fresh parsley.
