In a small bowl, combine all of the seasonings. Pat dry the pork butt, if there is any excess liquid. Drizzle with half the oil, then, press the seasonings into all sides of the pork.
Add the pork to the bottom of slow cooker. If there is a fat cap, put the fat cap placing up.
Slice the onion into big chunks. Add the lime juice, garlic and onion on top of the pork.
Cover the slow cooker pot and cook on low for four hours, or until the pork reaches 205 degrees.
Let the pork cool for a couple minutes, so it is not too hot to the touch. As the pork is cooling, heat the remaining oil in a pan over medium high heat.
Once the pork has slightly cooled, shred with a hand mixer or two forks. Add to the pan with the heated oil, cover, and let crisp for a couple minutes.
Once that side is crisped to your likeness, toss the pork and repeat this crisping process. Remove from heat once ready.
If there are any liquids still in the slow cooker, add those back into the pork and mix to allow the pork to absorb any juice.