Preheat oven to 225 degrees or turn on crockpot to medium. Preheat oil over medium heat in a large skillet.
Saute onions for 2 minutes or until they start becoming translucent. Pour in minced garlic and cook another minute.
Sprinkle salt and pepper over pork liberally. Push onions and garlic to the edges of the pan and sear meat on all sides until brown.
Transfer entire contents of the pan into a baking dish with high sides. Pour enchilada sauce over top, cover with foil and bake for 2-3 hours or until meat is fork-tender. Shred pork and serve in tacos, burritos, on nachos, etc.