Preheat oven to 350 degrees. In small saucepan, combine chicken, 1/4 cup onion, chopped tomato, garlic, salt, and enough water to cover chicken. Bring to boil; reduce heat. Simmer until tender. Let cool in broth. When cool, shred chicken and set aside. In bowl, mix chicken, enchilada sauce and 1/4 cup onion. Set aside.
Heat tortillas as directed on package. Place 1 teaspoon cheese, 2 tablespoons chicken and 1 teaspoon enchilada sauce mix on each tortilla. Roll and place in a 9 x 12 inch dish. Top with remaining sauce, cheese and sour cream. Bake 20 minutes or until bubbly. Makes 12.