Cook spaghetti and drain in cold water.
Grease large casserole dish with margarine or butter.
Chop up onion, shred cheese and chop up tomatoes a little.
Add half of drained spaghetti to casserole dish then add 1/2 of onion, 1/2 of tomatoes, 1/2 of cheese. Salt and pepper.
Repeat as before-spaghetti, onion, tomatoes, cheese, salt and pepper.
On top of this add the bacon uncooked-working outside in.
Add enough milk to bring the liquid 1/2 up the dish.
Bake in oven @ 350 for 1 1/2 hours.