Mexican Omelet

In an 8-in. skillet, saute tortilla in butter until softened, about 2 minutes. Meanwhile, beat eggs, water and salt in a bowl. Pour over tortilla in skillet; cook over medium heat. As eggs set, lift edges, letting uncooked portions flow underneath. When eggs are set, remove from the heat. Sprinkle with 3/4 cup cheese. Combine avocado, 1/2 cup sour cream, chiles and lemon juice; spread over half of the omelet. Fold omelet in half and transfer to a warm platter. Top with tomato and remaining cheese and sour cream. ');