The recipe I was given years ago lacked in flavor so I modified it and we're extremely happy with the outcome. I've been making them this way for years. Originally the roasting was done on a rack with water underneath and just a simple salt and pepper.
Now I use a large onion diced as my natural rack to protect the pork. The onions bake together and become an essential flavor to the dish. I place the pork roast on top of the onion pieces and surround it with a can of diced green chiles and 4-5 cloves of minced garlic. Then I pour a can of salsa verde enchilada sauce on top of the green chiles and onions. Cover it with foil and bake for 2 hours at 350°.
Then uncover it and bake another hour or until fork tender. Remove the roast to a cutting board and shred it into bite sized pieces.