Place potato slices in covered vegetable steamer; steam 12 minutes; drain and cool. Mix together mayonnaise, onion, soy sauce, oregano, garlic and parsley. Frost each potato slice with this mixture, and then dip it into cracker crumbs. Bake on cookie sheets at 350 degrees for 10 minutes. Sprinkle with Parmesan and serve hot.
To make as a casserole, cover bottom of casserole with potato slices, spread on mayonnaise mixture, then sprinkle on crumbs. Continue in layers until all ingredients are used. Bake at 350 degrees for 1 hour. Top with Parmesan and serve.