Preheat the oven to 350°F (175°C).

Sauté the chopped onion in butter until softened.

In a mixing bowl, combine the cooked and diced chicken, sautéed onion, softened cream cheese, and chopped green chilies.

Spoon the chicken mixture onto each flour tortilla and roll up tightly.

Place the rolled tortillas seam side down in a greased Pyrex baking dish.

In a separate bowl, combine the cream of chicken soup, water, and sour cream.

Pour the sauce over the top of the rolled tortillas.

Bake in the preheated oven for 35 to 40 minutes, or until the enchiladas are hot and bubbly.

Sprinkle shredded cheddar cheese over the top of the enchiladas.

Return to the oven and heat until the cheese is melted.

Serve the enchiladas hot, accompanied by rice and beans if desired.

Enchiladas may be frozen before adding cheese.