Prepare the rub by putting cumin, oregano and salt into a small bowl. Toss with a fork to combine.

Sprinkle the rub over the pork shoulder and use your fingers to massage the rub into the pork.

Heat a large skillet over medium-high heat. Put cooking oil into the skillet, and allow to heat. Add the pork to the skillet and sear until it is brown all over, about 7-10 minutes.

Put the pork into the slow cooker first. Then add the garlic, onion, lime and orange juice and water. Cook pork on low for 6-8 hours, until meat completely falls apart.

Take the pork out of the slow cooker, and shred the meat with a pair of tongs or two forks. Add as much juice from the slow cooker as needed to keep meat moist and juicy.