Squash casserole freezes both unbaked and after baking but I will say the texture is not quite the same as baking it immediately. It works best to hold out the topping until ready to bake to achieve that crispy, crunchy topping. Unbaked: Cover unbaked casserole with plastic wrap and aluminum foil and freeze up to 2 months. Thaw in refrigerator at least overnight and sprinkle with topping mixture. Bake, uncovered, at 350F for 35 minutes or until bubbly around edges. Baked: Let cool completely and follow freezing and thawing directions for unbaked casserole. Bake, uncovered, for 25 minutes or just until thoroughly heated in the middle.