1. Trim excess fat from the pork shoulder. 
2. In a small bowl, combine salt, pepper, oregano, and cumin. Rub the seasoning mixture evenly over the entire pork shoulder.
3. Place the pork shoulder in a slow cooker. Squeeze juice from the orange halves over the pork.
4. Add the juiced orange halves and bay leaves to the slow cooker. Cover and cook on low for about 6 hours, or until the pork is fork-tender and easily shreds. 
5. Use tongs or a slotted spoon to transfer the pork to a large bowl. Shred with two forks, then toss with some of the cooking juices to season to taste. Cover to keep warm and set aside.
6. Serve with warm tortillas and toppings of your choice.

*Whole muscle pork cuts are safe to eat when cooked to 145°F and allowed to rest for 3 minutes.