- Heat oil in large saucepan over medium-high heat. Add carrot, onion, and celery and cook, stirring occasionally, until vegetables are softened, about 5 minutes. Add garlic and cook, stirring constantly, until fragrant, 30 seconds.
- Add broth, water, and tomatoes and bring to boil. Stir in barley, mushrooms, and pepper and return to boil. Reduce heat and simmer, covered, stirring occasionally, until barley is almost tender, about 40 minutes.
- Stir in zucchini; cover and cook until barley and zucchini are tender, about 5 minutes longer. Remove from heat and stir in basil. Serve sprinkled with cheese.
- Per serving (1 cup soup and 1½ teaspoons cheese)
To store leftovers, transfer the soup to an airtight container and let cool. Cover and refrigerate up to 4 days or freeze up to 3 months.