Boil mirlitons in water until tender. Remove and cool, then cut in half.
Scoop out (careful not to damage shells!!) and mash pulp.
Brown onions and garlic in margarine. Add parsley, celery, shallots, green pepper, thyme, and bay leaf. Add bread crumbs, salt, pepper, and pulp. Mix well. Fry about 5 to 10 minutes, stirring often. Add tuna, mix well, and fry additional 5 min.