This is a great meal to prep ahead of time and cook later. Simply cook the ground beef first and layer the casserole accordingly. Once the casserole is ready to be put in the oven, cover it for freezer storage. A well stored casserole can be left in the freezer for three months. To cook the frozen casserole, simply pull the dish out of the freezer and let it thaw overnight. Once the casserole has thawed put it in the oven for 30 to 45 minutes. Until the tater tots have turned golden brown and are hot. The easiest way to store this casserole in the freezer is with a tin foil pan. This would allow the tin foil to be easily wrapped around the top to get a nice seal on the dish. When the time comes to cook the meal simply thaw it overnight and put it into the oven uncovered.