We are fortunate enough to live in an area where really good fresh fish is obtainable.
One of the things the supplier does is a bag of fish pieces, containing fresh salmon, smoked salmon, white fish etc in precut pieces. It makes an absolutely delicious fish pie. One of DH's all time favourites. Mine too.
I poach the fish in some milk with s&p added, along with some dill and bay leaf.
Put cooked fish in a casserole dish along with a couple of chopped hard boiled eggs. I sometimes add some prawns.
Make a cheese sauce, using the liquid the fish was poached in and add more if needed, add some dried mustard to the flour when making the sauce.
Top with cooked, sliced layered potato, then grated cheese and cook til golden brown and faintly crispy on top. Very good.