Place oil in a large skillet and warm over medium heat. Place the pork shoulder in the skillet, once it's hot, and cook for 4 to 5 minutes on each side until a nice sear forms. Transfer the pork to a 5-quart crock pot.
In a mixing bowl, stir together the onion slices, garlic, beer, lime juice, TABASCO® brand Green Pepper Sauce, lime zest, chili powder, oregano, salt, pepper, and cumin. Pour the marinade over the pork.
Cover the slow cooker and cook on HIGH for 4 to 5 hours. The pork should easily shred from the roast with a fork. (Cook on LOW for 7 to 8 hours.)
Transfer the pork to a cutting board or platter. Pull out the bone (you should be able to do this easily with your hands), and then use two forks to shred the pork. Serve immediately or store in an air-tight container in the fridge.
Notes
If you prefer not to use beer, you can substitute vegetable broth instead.You can discard the marinade after the pork is removed from the slow cooker or strain it and use it to make a sauce.