Cook the pasta shells in boiling water according to the packet instructions – it will take around 8 to 10 minutes. Drain and set aside.
Reconstitute the powdered milk with two cups of water. Set aside.
In a heavy-bottomed saucepan, melt the coconut oil. Add the flour and stir. Allow it to bubble for a minute, then remove from the stove.
Gradually pour in the milk, stirring to prevent the mixture from clumping. Return to a low heat and low stir for five minutes until the mixture has thickened.
Stir in the parmesan and processed cheese, then the mustard.
Open the can of tuna and drain off any water or oil. Flake the tuna and add to the white sauce mixture. Add in the cooked pasta shells and stir to combine. Serve half of the mixture immediately.
Spoon the remaining mixture into a large ceramic baking dish and cover with cheese and breadcrumbs. Once cool, cover with aluminium foil and place in the freezer until needed.
