Zucchini-Rice Soup

3 large or 4 medium zucchini, chopped
1/2 C chopped onion
2 cans (10 oz each) low-sodium chicken broth
2 C cooked brown rice
1/2 tsp rosemary
2 T lemon juice
1 C plain nonfat yogurt

Simmer zucchini and onion in chicken broth for 15 minutes or until zucchini is tender (add water just to cover zucchini if necessary). Purée soup in a blender or food processor; return to pot. Stir in rice, rosemary, lemon juice, and yogurt. Adjust seasonings to taste. Heat to serving temperature; do not boil.