For fish pie just google "fish pie" "mary berry" - brilliant recipe and very adaptable.
As for chest freezers - you need to be organised! Ours has separate cardboard boxes for raw meat/poultry, fish, fruit, veg and bread. The 3 top baskets are for home-cooked ready meals, sauces, gravy, soups etc. The last covid year has been brilliant for concentrating the mind on using up the odd bits and pieces that were lurking in the bottom of said freezer so it no longer contains items of dubious vintage!