Yes, you can freeze the cooked casserole in a sealed container or you can wrap a casserole dish with several layers of plastic wrap. Defrost overnight in the refrigerator. To reheat tuna casserole, use the microwave or reheat in the oven in a foil-wrapped dish at 350 F. Add a drizzle of milk or half an half as it reheats to loosen up the noodles and sauce.