In heavy soup pot melt butter or margarine and saute onions, celery and carrot with about 1 TBS of salt until soft
Stir in 1/2 cup broth and zucchini
Cook until zucchini is tender, 10 to 12 minutes
Add remaining broth and simmer slowly until vegetables are tender, but still hold their shapes
Season to taste
Serve hot, sprinkled with cheese if desired
For a professional touch, add chopped fresh garlic in the beginning, and chopped basil at the finish.