Boil mirlitons until tender. Cut in half and remove seed and any stringy pulp near it. Scoop out pulp leaving a small amount on skin. Lightly salt and pepper inside of skins and set aside. Mash pulp. Saut? for 15 minutes stirring often. Next add shrimp, salt, Tobasco, green onion tops, parsley, and garlic powder. Stir well and let cook 5 minutes. Add ? cup seasoned bread crumbs and remove from heat. Stir well. Spoon a generous helping of dressing into each shell and arrange them in a baking pan. Sprinkle extra bread crumbs on top and put a pat of butter on each one. Add 1 cup of water to the pan and cover loosely with foil. Bake at 350? for 1 hour. Uncover and cook another 10 minutes to brown tops. Serve warm as a main dish.