Slice roast into 1½-inch slices, the cut each slice in half. Add to slow-cooker along with garlic pepper and oregano. Toss to get some of the spice mixture on all pieces of pork. Place onion wedges on top of pork.
Cook on low setting until meat is very tender, about 6 hours. Discard onion and shred pork. Serve with Homemade Corn Tortillas and Roasted Tomatillo Salsa.
If you don't feel like making homemade tortillas and/or salsa, substitute store-bought tortillas and prepared salsa verde.
Nutritional information is for pork only; it does not include the tortillas or salsa.