Combine sausage and onion in a large skillet; cook until sausage is browned and onion is tender. Drain well. Combine next 6 ingredients in a large mixing bowl; add sausage mixture to stuffing mixture, stirring until well combined.
Remove giblets from hens; reserve for other uses. Rinse hens with cold water, and pat dry. Sprinkle with salt. Stuff hens lightly with stuffing mixture. Close cavities, and secure with wooden picks; truss. Brush hens with melted butter, and place breast side up in a shallow roasting pan. Bake at 350° for 1 1/4 to 1 1/2 hours, depending on size of hens; baste often with melted butter. Garnish with lemon slices and parsley, if desired.