In a large skillet, heat the oil.
Salt and pepper the pork loin.
Add pork in the oil and sear on all sides.
Add the sliced onions to the bottom of the slow cooker.
Place the seared pork loin on top of the onions.
In a small bowl, whisk together the honey, soy sauce, lime juice, garlic, and chipotle.
Pour the marinade over the pork.
Set the slow cooker for 6-8 hours on low, or 4-6 hours on high, or until the thermometer reads 160 degrees.
Once the pork is ready, let the meat cool slightly before slicing.
Top with juices from the slow cooker, onions, lime and cilantro (if using).