1. In a 9- x 13-inch baking dish, arrange potatoes, onions, carrots and zucchini. Add one-fourth cup water or liquid from mushrooms. Dot with margarine and sprinkle with salt and pepper.
2. Cover with aluminum foil and bake in a preheated oven at 350 degrees for one hour.
3. Add mushrooms and fish and sprinkle with lemon juice. Bake, uncovered, for additional 30 minutes.