Combine the salt, black pepper, cumin, chili powder and olive oil/bacon fat and rub it over the pork shoulder.
Transfer the pork to the slow cooker (fat cap up) and add the diced onions, garlic and orange juice.
Cook on low for 8-10 hours or on high for 5-6 hours.
The meat should be very easy to shred with a fork at this point.
Gently remove the meat from the slow cooker and set aside.
Reserve the left over juices by skimming off the layer of fat and setting aside.
Shred the meat using 2 forks.
OPTIONAL - to crisp up the carnitas, place in the oven on broil for 5 minutes.
When ready to serve, pour a little of the reserve juice over the pork and enjoy!