I've made this a number of times; not my favorite kind of casserole, but they liked it - grew up on it.

One large can of tuna, drained

large pkg. of cream cheese, softened

one egg

1/2 C milk

croutons
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Mix cream cheese with tuna, put in casserole.

whisk egg and milk, pour over tuna mixture.

top with croutons

Bake at 350 20-25 minutes uncovered till completely baked through and croutons slightly browned.

Make them spinach.

Oh, forgot, with the tuna and cream cheese you add a stalk of celery cut up. That adds some texture, especially if you don't have noodles. I would have both, myself.

To feed a family of 6 on a skimpy food budget, my mom used whatever we had on hand, cooked noodles or rice, canned cream soups, sometimes chopped onions or celery, and the one small can of tuna. On occasion, there might be a sprinkle of grated cheese, breadcrumbs or crushed potato chips on top.

We loved that stuff, it was comfort food, all bubbly hot and gooey from the oven, and my own kids also grew up eating that same tuna casserole, passing on the tradition by serving it to their own families.

1 can tuna
1 can cream of something soup; mushroom, celery, whatever
one stalk of celery minced fine and onion too (optional)

Cook pasta or noodles, drain and mix everything else in while still hot.

I sauté fresh mushrooms and onions in a little butter, then add a can of mushroom soup and some sour cream, then a large can of drained albacore tune and then some cooked rotini pasta. I put it in a casserole with some crumbs and a sprinkle of paprika on the top and cook for about half an hour on 350.

Mushroom Soup. My mother never made this because she hated fish, but I ate plenty of it when I was growing up--school cafeteria, friends' houses, etc.

https://www.campbells.com/kitchen/recipes/classic-tuna-noodle-casserole/

ETA: Back in the day, it was always crushed potato chips on top--not buttered bread crumbs.

What I have in the pantry or the freezer, or what has been on sale recently

One or two cans of tuna, drained (give juice to cats)
a box or two of macaroni & cheese, often the store brand
can of condensed soup - cream of mushroom or celery, or cheddar & broccoli
16 ounce bag of frozen vegetables - with broccoli, cauliflower and carrots, usually
cheese - usually sharp cheddar but whatever is in the fridge
can of mushrooms, drained
maybe some chopped onion, bell pepper, celery if I have some around
salt free herb mixture or put in whatever I'm in the mood for. I generally do NOT add any salt to my casseroles.

Cook frozen vegetables according to package directions, just partway. Prepare the mac & cheese according to box directions. Saute any chopped fresh vegetables. Mix everything together - add seasonings to taste. Bake in the oven at 350 F until hot and bubbly. Sprinkle more cheese and some paprika on top and put back in oven until the cheese melts.

Not fancy but easy and it's one of my comfort food go-tos.