In large skillet, saute' onion and green peppers in butter until tender. Add tomatoes, mushrooms, olives and oregano. Add ground beef. Simmer uncovered for 10 minutes. Place half of the spaghetti in a greased 9 x 13 baking dish. Top with half of the vegetable/meat mixture. Top with 1 cup Cheddar cheese. Repeat layers. Mix soup with water until smooth and pour over casserole. Sprinkle with Parmesan cheese. Bake uncovered at 350 for 30 to 35 minutes or until heated through.