Preheat oven to 350° F. Make a white sauce with the butter or margarine, flour, milk, and salt. Add 3/4 cup of the cheese and stir till melted. Brown sausage in a skillet. Add the zucchini, onion, and mushrooms. Saute till tender. Drain any excess grease. Stir in sauce, noodles, and tomatoes. Pour into a 1 quart casserole. Top with remaining cheese. Bake at 350° F for 20 minutes.