Salt both sides of the roast thoroughly. In a small bowl, combine olive oil, garlic, cumin, black pepper and oregano together. Coat roast with olive oil mixture. (This can be done the night before to save time in the morning.)
Place pork roast into slow cooker with of water and onions and turn heat to high. Cook 8- 9 hours or until meat is pull-apart tender. (Roast should barely be covered with water. Adjust water to the appropriate level.)
Set aside 2 cups for tonights dinner. Shred the remaining pork and store in freezer safe bags or containers and freeze in 2 cup portions.
The liquid left over from this roast can be used as stock or broth in future recipes. Simply cool in the refrigerator overnight. In the morning skim off any fat that has accumulated on top, and store remaining liquid in 1 or 2 cup portions in freezer safe bags or containers for fast and easy future use.