Freeze it after cooking. By that time all the ingredients will have blended and cooked meat or seafood (if seafood lasagna) can stay longer in the freezer. The meat and noodles have different thaw rates, it is better to let it thaw naturally than using the defost in the miocrowave or oven. Also, it is better to freeze individual portions than a brick of lasagna. If you made extra tomato sauce to put on top of the lasagna for serving, freeze it separately, don't combine it by putting it on top and then freezing - when it thaws, it just gets glooply. Also, the easiest way to store both is in separate plastic sandwich-sized bags.