buy large handful of fish pie mix (that's chunks of fish not a packet) from supermarket fish counter or one large fillet of haddock (smoked or not up to you)
Turn on oven to 180. Boil sliced potatoes until soft, drain and then mash. In oven proof dish tip in 1/3rd tin of cream of mushroom soup or seafood chowder. Add 1/2 finely chopped leek and generous quantity of spinach. Add fish pie pie mix. Layer mash potato on top. finish with layer of grated cheddar. Pop in oven. Ready in 30 mins.
If you use fillet of fish instead of the chopped mix just cook that in water or milk at same time you are making the mash. then take off skin, pick out any bones and chop into pieces to go in dish as before.