Prepare the Pork: Thoroughly rinse the pork shoulder roast and pat it completely dry with paper towels.
Mix the Spice Rub: In a small bowl, combine the kosher salt, dried oregano, ground cumin, freshly ground black pepper, smoked paprika, and olive oil. Stir these ingredients together until they form a cohesive paste.
Season the Roast: Generously rub the entire surface of the pork roast with the prepared spice mixture, ensuring it's evenly coated.
Layer in Slow Cooker: Position the seasoned pork roast in the slow cooker, preferably with the fattier side facing upwards. Distribute the thinly sliced yellow onion and minced garlic over the top of the pork. Pour the fresh orange juice evenly over the roast and aromatics.
Slow Cook: Secure the lid on the slow cooker. Cook on the LOW heat setting for 8 to 9 hours, or until the pork is exceptionally tender and can be easily shredded with a fork.
Shred the Pork: If a significant fat cap remains intact on top of the roast, carefully remove and discard the largest pieces. Gently pull the pork apart into bite-sized pieces and chunks directly in the slow cooker or after transferring to a large bowl. Avoid over-shredding into tiny pieces to maintain a good texture. Using a slotted spoon or tongs, remove the shredded pork from the slow cooker, allowing excess liquid to drain back into the pot. Reserve the cooking juices.
Crisp the Pork: Heat a large, heavy-bottomed non-stick skillet or cast-iron pan over medium-high to high heat. Once hot, add approximately 1.5 to 2 cups of the shredded pork to the skillet in a single layer (avoid overcrowding). Press down lightly with a spatula to encourage browning. Cook for about 2-3 minutes per side, or until the pork achieves a crispy, browned exterior.
Serve: Transfer the crisped pork to a serving platter. Moisten the pork by drizzling a few spoonfuls of the reserved cooking juices from the slow cooker over it. Repeat the crisping process with any remaining pork. Serve warm.