tuna casserole

so i'm on a bit of a tuna kick. i've been craving this lately and i don't know why. it's good.

1-2 cans tuna packed in water {drained}--depending on how tuna-y you like it
1 can cream of chicken soup
1/2-1 can milk
a couple spoonfuls sour cream
1/2 chopped onion
1 small bag frozen peas
1 bag cooked and drained small shell pasta
1-2 cups grated cheese
1 sleeve ritz crackers crushed
2-3 TBS butter melted
salt
pepper

mix first seven ingredients. add more sour cream or milk to fix consistency as needed {not too sticky, not too soupy}. pour into a casserole dish {9x13 works well} sprinkle liberally with pepper and salt and top with grated cheese. mix ritz and melted butter and sprinkle over cheese. cook at 350 degrees until cheese is melted, cracker crumbs are browned and filling is bubbly {about 15-20 minutes}