Using a mortar and pestle, crush cumin seeds until finely ground. Add garlic to the mortar and pestle, then pound until the garlic and cumin have made a paste (Alternatively you could use 3/4 teaspoon ground cumin and 3 minced cloves garlic if you do not have access to mortar and pestle. The flavor will not be as strong, but still very good.) Stir in the oregano, ground oregano, sea salt and 2 teaspoons olive oil. Rub this mixture into the pork shoulder really well using your hands.

Place pork into a large ziploc bag and pour in citrus juice. Seal, then massage a bit to work the juice throughout the pork. Place bag in the refrigerator and let marinate for at least 6 hours, best if overnight.

After it has marinated, preheat oven to 225 degrees F or turn on slow-cooker to low. Then heat remaining 1 tablespoon olive oil in a large dutch oven to medium high (something big enough so that the meat can lay flat inside it). Sear pork shoulder on both sides for 4 minutes, until slightly browned.

Add leftover citrus juice from the bag to the dutch oven, then place in oven, covered, and roast for 6-8 hours, basting with its own juices every 2 hours. OR you can add the seared pork and remaining citrus juice from bag into the slow-cooker and roast on low for 6-8 hours, basting with its own juices every 2 hours. When done roasting, shred the pork in its own juices and transfer to a container.