Season the pork with salt and pepper and place in slow cooker.
Add the jalapeno, onion, BBQ sauce and pineapple juice to the slow cooker and cook on low for 8 hours.
Remove the pork from the slow cooker, shred using two forks and return the meat to the slow cooker to absorb the juices.
Heat the oven to 450 degrees and line two baking sheets with tin foil.
Spread the pork (letting any excess juice drip off back into the slow cooker) in an even layer on the baking sheets. Cook for 15-20 minutes until the ends of the pork start to turn golden brown and get crispy.
While the pork crisps, place a large skillet over medium high heat.
Once hot, add the spicy pickled pineapple slices to the skillet and cook for 2-3 minutes per side until golden brown and starting to caramelize. You can add some extra juice from the slow cooker to the skillet as the pineapple cooks for extra flavor.
Assemble the pork, pineapple slices and cilantro on sandwich rolls and serve.