Preheat the oven to 350° F.
Spray a 9x13 inch baking dish with cooking spray.
Remove the chicken from the bone (if using a rotisserie chicken) and shred by using two forks. Place the shredded chicken into a large bowl. *Make sure your chicken is room temperature or warm, if using leftover cold chicken, heat in the microwave until just warmed…cold chicken baked in a casserole dish doesn’t get as hot when baking and will result in a lukewarm center.
Add the fiesta blend shredded cheese, Rotel sour cream and the chicken fajita seasonings to the bowl. Mix together until combined.
Evenly divide the chicken filling between each of the flour tortillas. Roll the filled tortilla shells and place each one seam side down in the prepared baking dish as you go.
In a saucepan, melt the butter, then whisk in the flour and allow roux to thicken for about 45 seconds, stirring constantly.
Add chicken broth, bring to a low simmer, and whisk until smooth.
Next, add the sour cream and diced green chilies. Stir continuously until the sour cream is dissolved and the sauce is warm.
Pour the sour cream sauce over the tortillas and top with the Monterey Jack shredded cheese.
Bake covered for 45 minutes or until golden and bubbly..If you like, remove the foil, then turn on the broiler after the enchiladas are finished baking broil for an additional 1-2 minutes to achieve a crispy topping.