Grease 5 quart baking dish. Place potatoes on bottom of pan and top with a layer of broccoli and mushrooms. Mix together next 4 ingredients and season with salt and pepper. Pour over vegetables. Bake at 350 for one hour. Pull out of oven and place tomato slices over top and sprinkle with cheese. Return to over for 8-10 minutes. Allow to sit for 5 minutes before serving.
Makes 12 servings.