Grease covered casserole pan. Thinly slice squash into pan. Sprinkle with salt & pepper & dab with butter. Thinly slice tomato on top, s & p & butter again. Thinly slice onion and place lots on top. Add more S & P & B. Cover and bake for 30 – 40 minutes covered (until onion is cooked and limped). Then take off lid – thickly sprinkle on parmesan cheese and crushed crackers. Bake for another 45 minutes or until top is browned. Mmmmmm good!