Saute one onion and ½ clove garlic in butter. Place in crock pot with a small roast or ~2lbs round streak and cook for 6-8 hours. Shred beef and add 3 chopped tomatoes and 1 (28oz.) can green chilis. Sprinkle a pinch of oregano and cumin and mix well. Serve as burritos with desired toppings.