Cut squash in half lengthwise, and remove seeds. Place cut side down in a shallow baking dish and add 1/2 inch boiling water. Bake at 375 degrees for 35 minutes. Turn cut side up and sprinke with salt; set aside.
Cook sausage and onion in a skillet until browned, stirring to crumble meat; drain. Stir in breadcrumbs; spoon into squash cavities.