In the morning, place the pork in the slow cooker and cover mostly with water. Add the onions, garlic, oregano, and cumin to the water and around the pork. Turn the slow cooker on HIGH for several hours (5 or 6), or cook on LOW for at least 8 hours. The meat should be tender and pull apart easily when done.
Just before serving, remove the meat from the slow cooker with a slotted spoon and place in a foil-lined pan. The meat should literally fall off the bone. Reserve some of the onions and discard the water. Sprinkle the meat with garlic powder. Broil the meat, fatty side up, for 5 more minutes so the meat is crispy on the outside. Watch so that it does not burn.
Remove from the broiler. Shred the meat with two forks, discarding any fat that remains. Place in a casserole dish and add the reserved onions. Keep warm until ready to serve.
When ready to serve, place the meat, tortillas and all desired condiments in bowls that can be self-served, either buffet style or on the table. Have the pork on its own, or tucked into tortillas with condiments.
Notes
Nutritional information does not include tortillas or condiments.