In a blender, combine the pineapple juice, quartered onion, garlic cloves, chipotle peppers, adobo sauce, apple cider vinegar, achiote paste, cumin, oregano, smoked paprika, salt, and pepper. Blend on high until the marinade is completely smooth.

Pat the pork shoulder chunks dry with a paper towel. Heat the vegetable oil in a large skillet over medium-high heat. Working in batches, sear the pork chunks on all sides until well-browned, about 2-3 minutes per side. Transfer the seared pork to the Crockpot.

Pour the blended marinade over the seared pork in the Crockpot. Add the 1/2 cup of chopped pineapple and the bay leaf. Stir gently to ensure all pork is coated.

Cover the Crockpot and cook on HIGH for 4-5 hours or on LOW for 6-8 hours, until the pork is exceptionally tender and easily pulls apart with a fork.

Carefully remove the pork from the Crockpot and place it on a large cutting board or baking sheet. Discard the bay leaf from the sauce. Allow the pork to rest for 5-10 minutes.

Using two forks, shred the pork into bite-sized pieces.

For the authentic crispy edges (optional but highly recommended): Preheat your oven's broiler to high. Spread the shredded pork in a single layer on a baking sheet. Drizzle with 1/2 cup of the sauce from the Crockpot. Broil for 3-5 minutes, watching very closely, until the edges of the pork are slightly crispy and caramelized.

Return the crisped pork to the Crockpot with the remaining sauce and stir to combine. Keep the Crockpot on the 'Warm' setting.

Assemble your tacos by filling warm corn tortillas with the al pastor pork. Garnish generously with fresh diced pineapple, chopped white onion, cilantro, and a squeeze of fresh lime juice.