Remove rolls from package and cut horizontally, creating 1 top and 1 bottom. Bring butter,mustard,onion and poppy seeds to a boil, reduce heat to low until onion's are tender. With a pastry brush, brush mixture on both sided of rolls. top with chopped ham and Swiss, should take 3 slices of Swiss cheese lengthwise. wrap in aluminum foil and bake at 350 degrees for 20 to 25 minutes. These can be made ahead of time and put in the refrigerator.