Sear the Pork
Begin by heating the oil in a large Dutch oven over medium-high heat. Lightly season the pork pieces with salt, then add them to the pot in batches, ensuring they aren’t crowded. Sear the pork on all sides until browned, about 8 to 10 minutes. Once browned, transfer the pork to a 5- to 8-quart slow cooker. Pour off any excess fat from the pot but be sure to reserve it; do not wash the pot.
Slow-Cook the Pork
Add the pickled jalapeño brine to the slow cooker, approximately ¾ cup, and then stir in the fish sauce. Cover the cooker and cook on low heat for 4 to 6 hours, or until the pork shreds easily with a fork.
Make the Glaze
After the pork has cooked, spoon off the fat from the liquid in the slow cooker. Pour 1 cup of this liquid into the reserved Dutch oven, then stir in the brown sugar and pickled jalapeño slices, adjusting the quantity to suit your heat preference. Simmer the mixture over medium-high heat, scraping the pot’s bottom, until the sauce thickens and reduces by half, about 7 to 9 minutes, resulting in a syrup-like glaze.
Shred the Pork and Combine
Using two forks, shred the pork directly in the slow cooker into bite-sized pieces. Once the pork is shredded, stir the reduced sauce into the meat, ensuring it is well-coated. Serve and enjoy.