In a small saucepan, whisk together sauce ingredients. Bring to a simmer over medium-high and cook for 1 to 2 minutes, or until mixture is thick and bubbly; set aside.
Preheat oven to 350° F (175° C). Lightly spray a 9"x13" baking dish with non-stick cooking spray.
In a medium non-stick skillet, combine chicken, cream cheese and salsa. Cook over medium-low heat for 5 to 6 minutes, or until mixture is warmed through and cream cheese has melted, stirring occasionally.
Wrap tortillas in damp paper towels and microwave on high for about 1minute or until hot.
To assemble, pour 1/2 cup of sauce into baking dish; spread to cover the bottom of the dish. Put a tortilla on a plate and spoon about 1/4 cup of chicken mixture onto middle of tortilla. Roll tortilla jelly-roll style and place seam side down in baking dish. Repeat with remaining tortillas and filling.
Pour remaining sauce over enchiladas. Cover with foil. Bake for 10 minutes.
Meanwhile, in a small bowl, whisk together sour cream, lemon juice and chili powder.
When enchiladas have baked for 10 minutes, remove from oven and spread sour cream mixture on top of enchiladas. Sprinkle with nonfat cheddar cheese and additional chili powder, if desired. Bake, uncovered, for 5 minutes.
There are 260 calories in 1 serving of Sour Cream Chicken Enchiladas.