Stir together the olive oil, salt, pepper, oregano, and cumin. Rub the spice mixture over the pork roast. Place the roast in the slow-cooker with the fat cap facing up. Place the onions, oranges, limes and garlic in the crock pot. Pour the water or orange juice over the roast.
Cover with lid and cook on LOW for 9-11 hours, until tender and falling apart. Carefully pull apart the roast, discarding extra fat. Use a slotted spoon, spatula, or tongs to lift the meat out of the slow-cooker.
Place the pork on metal baking sheets and shred as desired. Place under the broiler until meat starts to crisp.
Transfer to a serving dish and drizzle with some of the juices from the slow-cooker. Serve with avocado buttermilk ranch, pickled onions and spicy slaw.