In a large skillet, sauté onion and green pepper in butter until tender. Add undrained tomatoes, mushrooms, olives, oregano, salt and pepper. Add ground beef and simmer, uncovered, for 10 minutes. Place half of the spaghetti in a greased 13"×9" baking dish. Top with half of the vegetable mixture. Sprinkle with one cup of Cheddar cheese. Repeat layers. Combine soup and water; stir until smooth. Pour over casserole. Sprinkle with Parmesan cheese. Bake, uncovered, at 350 degrees for 30 to 55 minutes, or until heated through.