The casserole can be assembled and baked immediately or covered and refrigerated overnight before baking.
If the casserole is refrigerated overnight, remove it from the fridge 30 minutes before baking. It may require an extra 10-15 minutes of cooking time.
Veggies can be substituted for the sausage. If using water-filled veggies, like mushrooms and spinach, make sure that they are cooked and drained to remove the excess moisture.