combine squash and water to cover in a medium saucepan; bring to a boil. cover, reduce heat, and simmer 10 minutes or until tender. drain well, and mash; set aside.
sautÉ onion in butter until tender. combine onion, squash, ¾ cup cracker crumbs, cheese and remaining 5 ingredients. spoon into a lightly greased 2-quart casserole or an 11x7-inch basking dish. sprinkle with remaining ½ cracker crumbs. bake, uncovered at 350 for 45 minutes.