Slice zucchini into 1/2 inch pieces and drop into boiling water. Cook 4-5 minutes and drain. Place zucchini in casserole dish. Saute onion and green pepper in margarine.
Add sauce mix, cheddar cheese, mushrooms, tomato paste, and water. Mix well and pour over zucchini. Sprinkle top with Parmesan cheese. Bake 25 - 30 minutes at 350°, or microwave 13 minutes on HIGH; turn once. Let stand 5 - 10 minutes before serving.