Preheat the oven to 350 degrees F (175 degrees C). Grease an 11×15 inch baking dish with nonstick spray.

Place chicken breasts in a large saucepan with enough water to barely cover them. Bring to a boil over medium heat.

Reduce heat to medium-low and simmer until the chicken is no longer pink in the center, about 15 minutes. Remove from the saucepan, drain, and shred the chicken with 2 forks.

In a large bowl, mix the shredded chicken with 1 package of Colby Monterey Jack cheese and the chopped green chilies (if using).

Spoon about 3 tablespoons of the chicken mixture down the center of each tortilla and fold it in half, enclosing the filling. Roll the folded tortilla into a cylinder.

Place each enchilada seam side down in the prepared baking dish.

In another bowl, whisk together the cream of chicken soup, half and half, chicken broth, and about 1/3 of the remaining cheese until well combined.

Pour this mixture over the enchiladas, then sprinkle the rest of the cheese on top.

Let the dish stand for 10 to 15 minutes.

Bake in the preheated oven until bubbly and the cheese topping is melted and beginning to brown, about 25 minutes.