Cut off and discard the top and bottom of the pineapple, then peel and core it, reserving 4 to 6 strips of the peel. Slice the pineapple into 1/2-inch rings. Set half aside, reserving for later, and chop the remaining pineapple into 1/2-inch chunks.

In a small bowl, stir together the garlic, oil, chili powder, cumin, oregano, black pepper, and 1 tablespoon of the salt. Rub the spice mixture all over the pork shoulder and transfer it to a 6-quart slow cooker.

In a medium bowl, combine the chopped pineapple, yellow onion, chipotle peppers in adobo, 2 tablespoons of the vinegar, and 1/2 cup water. Pour over the pork, then add the reserved pineapple peel, cut-side down. Cover and cook until the pork can be easily shredded with two forks, on high for about 6 hours or on low for 8 to 10 hours.

Meanwhile, in a small pot, combine the brown sugar, 1/2 cup of water, and the remaining 1 teaspoon salt and 1/2 cup vinegar, and bring to a simmer, stirring to dissolve the brown sugar and salt. Transfer the red onion to a glass jar or other heat-safe container. When the vinegar mixture is ready, carefully pour it over the onions, pressing down with a spoon to submerge them completely. Set aside to cool to room temperature, about 30 minutes. Cover and set aside until ready to serve (any leftover pickled red onion will keep, refrigerated, for up to 2 weeks).

When the pork is ready, shred completely and cover to keep warm.

Working in batches, lightly char the tortillas over an open flame if you have a gas stove, or in a large skillet over high heat, about 30 seconds per side. Transfer to a clean kitchen towel or aluminum foil packet to hold warm until ready to serve.

Heat a large skillet over medium-high heat. Add a drizzle of oil to the pan. When it shimmers, add the reserved pineapple rings, working in batches, and cook until golden and beginning to caramelize, 2 to 3 minutes per side. Transfer to a cutting board and allow to cool slightly.

Meanwhile, heat a drizzle of oil in another large pan. Add about 3 cups of the shredded pork mixture, along with 1/4 cup of the juices from the slow cooker, and cook, undisturbed in an even layer, until crisp, 5 to 7 minutes, working in batches as necessary depending on how many people you're serving. While the pork crisps up, finely chop the caramelized pineapple and transfer to a bowl for serving.

Build tacos using the warm tortillas, crispy pork, charred pineapple, pickled red onions, cilantro, and lime wedges.