Heat oven to 350. Grease 2-quart casserole. Cut potatoes into thin slices. Layer half each of the potato slices, onion, fish, margarine, parsley and pepper in casserole. Repeat layers. Pour water over layers in casserole; cover. Bake until potatoes are tender, about 1-1/4 hours. Serve with margarine and snipped fresh parsley, if desired.
(From a recipe in "Cleaning and Cooking Fish" by Sylvia Bashline)