In a large saucepan, sauté grated zucchini, celery, and onion in hot oil for about 6 minutes, until celery is just tender.
Add tomato sauce, water, tomatoes (with juice), chili powder, garlic salt, salt, sugar, and pepper.
Simmer slowly, uncovered, for 90 minutes.
Add olives, kidney beans, and mushrooms.
Simmer for another 10 to 15 minutes and serve.