10 to 12 tomatillos, husks removed and cut in half
1/2 medium onion, quartered
2 cloves garlic, finely chopped
2 serrano or jalapeño peppers
2 tablespoons cilantro, chopped
1/4 teaspoon salt
1/4 cup low fat sour cream (or Homemade Sour Cream)
juice of 2 limes
Combine the oil, juice from one lime, oregano, and black pepper in a shallow glass baking dish. Stir. Place the chicken breasts in the baking dish and turn to coat each side. Cover the dish and refrigerate overnight. Turn the chicken periodically to marinate chicken on both sides.
Put water, tomatillos, and onion into a saucepan. Bring to a gentle boil and cook uncovered for 10 minutes or until the tomatillos are tender. In a blender, place the cooked onion, tomatillos, and any remaining water. Add the garlic, peppers, cilantro, salt, and the remaining lime juice. Blend until all the ingredients are smooth. Place the sauce in a bowl and refrigerate.
Place the chicken breasts on a hot grill and cook until done. Place the chicken on a serving platter.
Spoon a tablespoon of low fat sour cream over each chicken breast. Pour the sauce over the sour cream.