I do fish pie quite often...make a huge pile of mash, boil the eggs, make a vat of thick bechamel sauce and let them all cool
Cut up your fish, then I shake a single layer of peas (frozen) into the dish, add raw fish chunks and quartered eggs, some peeled prawns if you have them, put a nice layer of sauce over, then add the mash and freeze
I have those glass freezer to oven dishes with the snappy lids and they are just brilliant for stuff like this.
You can defrost and cook or just do from frozen.
I also freeze left over mash to use for cottage pies or cheesey mash, it does want to be reheated in the oven though or it's peculiar, like instant mash, but it comes up a treat in the oven!
Often do a job lot of chicken for Hunter's chicken...cut the chicken breasts almost in half so they open like a book....add some cheese, close up chicken and wrap around a couple of bits of streaky bacon. I lay them on a tray to freeze and then box or bag them once solid. I lift them out to defrost, and either use jar sauce or make my own...usually serve this with cheesey mash from the freezer too. You can use chicken thighs, but you'd need a couple of big ones per person, so it's faffier
Make bolognaise, have with spaghetti, use remainder for a lasagne, get it all made in a dish and leave it in the freezer for next week. Another thing I used to do was if the bolognaise was too runny then save the gravy, leave a little of the mince in it, and make beefaroni, mix in macaroni with the gravy, cut up some mozzarella and poke it in, thick cheese sauce layer on top and serve with garlic bread.
Sausage rolls too or a big giant one, I make them but only cook the ones we are eating that night, freeze the others uncooked. If you squish the meat out of sausages, add S&P, some herbs, a grated apple and some parmesan they are really tasty. A spoonful of chutney never hurts either!
It's about cooking/prepping once to get as many different meals as possible rather than making enough of something to last you till doomsday.