The casserole can be assembled up to a day in advance and refrigerated before baking. Just remember to remove it from the refrigerator about 45 minutes before putting it in the oven so that it is not too chilly when baked.
Vegetarian variation: Make a vegetarian variety of this dish by substituting 4 cups of sliced white mushrooms sauteed in a bit of oil for the chicken and using condensed cream of mushroom soup instead of cream of chicken.