Remove ends of squash and discard. Chop or cut squash into small fine pieces. Add salt to water and boil squash and onion until tender for approximately 15 minutes. Drain well.
In a medium size bowl, mix cheese with squash mixture. Beat eggs and stir into milk. Add to squash mixture.
Pour one-half of squash mixture into a 2 quart casserole baking dish. Sprinkle 1/2 cup of cracker crumbs over and pour 1/2 of melted butter. Pour remaining squash mixture and repeat with remaining crumbs and melted butter on top.