1. Cook, skin and bone a whole chicken. Pull meat off in thin strips.
2. Preheat oven to 350°.
3. In a saucepan, cook onion and garlic in butter until onion is transparent. Reduce heat and simmer uncovered for 20 minutes. Remove from heat.
4. Dip each tortilla into tomato mixture.
5. Place strips of chicken and two tablespoons of shredded cheese on each tortilla, roll up and place seam side down in a 13x9-inch baking dish that has been coated with cooking spray.
6. Blend sour cream into remaining tomato mixture and pour over tortillas