Cut pork shoulder into large 4-inch chunks, removing any excess fat. Place in the slow cooker.
Add all the other herbs/spices to the slow cooker and mix thoroughly, coating the meat.
Cover and cook on high for 4 hours or on low for 6-8 hours. When tender, shred the meat by pulling it apart with a fork.
Serve pork carnitas on warm corn tortillas and top with onions, cilantro, lime juice and any other toppings you desire.