Trim any excess fat from the edges of the roast. Place roast on a sheet of heavy duty foil large enough to enclose the meat. In a small bowl, combine the green chiles, chili powder, oregano, cumin, garlic, salt and pepper to taste. Mix well and rub over both sides of the meat. Enclose the meat in the foil and then wrap the foil package in a another sheet of foil so it has a double layer. Place in a large baking or roasting pan.
Bake at 300 degrees for 4-1/2 to 5 hours, or until the roast just falls apart with a fork. Remove from oven, open the foil package and shred the meat. Carefully remove foil from pan and transfer the meat and cooking liquid into the pan. Use in tacos, burritos, or enchiladas.
Crock pot method: After wrapping the roast in foil, transfer to the crock pot. Cook on low for 8 to 10 hours. Remove foil and shred meat into the cooking sauce in the crock pot. Serve.
Make ahead method: This beef is fantastic when reheated with sauce it makes while cooking. If you want to really save time, make a day or two in advance, cover the pan with foil or plastic wrap and refrigerate till needed. Reheat in microwave and serve.