Once they have cooled, place the chicken breasts on a cookie sheet in a single layer and set in the freezer for 2 hours. At that point I like to stack them in a freezeable plastic container, but I have also made piles in the center of a piece of tinfoil and wrapped them up. It works either way. The important thing is to leave the sauce and cheese off until you are ready to bake. That helps keep them crispy.