I used reduced fat sour cream and olive oil instead of vegetable oil.
1 lb chicken breast, diced
1 medium onion, chopped
1 tablespoon vegetable oil
8 flour tortillas, softened (8 inches each)
1 1/2 cups grated monterey jack cheese or 1 1/2 cups Mexican blend cheese, divided
1/4 cup butter
1/4 cup flour
1 (15 ounce) can chicken broth
1 cup sour cream
1 (4 ounce) can chopped green chilies
In frypan, cook chicken and onion together in oil over medium-high heat until chicken is just done.
Divide cooked chicken evenly between 8 tortillas; add 1 1/2 tablespoons cheese to each tortilla.
Roll enchiladas and place seam-side down in 9×13″ baking dish that has been lightly sprayed with no-stick cooking spray.
Melt butter in a medium saucepan; stir in flour to make a roux; stir and cook until bubbly; gradually whisk in chicken broth then bring to boiling, stirring frequently.
Remove from heat; stir in sour cream and green chiles; pour sauce evenly over enchiladas.
Top with remaining 3/4 cup cheese (baking dish may be double-wrapped and frozen at this point) and bake at 400F for 20 minutes until cheese is melted and sauce near edges of baking dish is bubbly.