1. Heat oil in large pot or Dutch oven over medium heat. Add onion and garlic, and sauté 4 minutes, or until softened. Add carrots and celery, and cook 5 minutes, stirring occasionally. Stir in tomatoes, add thyme sprigs, and cook 2 minutes more.
2. Smash 1/2 cup chickpeas with back of a fork to form paste. Add smashed and whole chickpeas, broth, and 2 cups water to pot. Bring to a boil, then reduce heat to medium-low, and simmer 5 minutes. Add ditalini and basil, and cook 7 to 8 minutes, stirring occasionally.
3. Thin soup with broth or water (if necessary), and adjust seasoning. Remove thyme sprigs, and serve garnished with shredded basil and sprinkled with Parmesan cheese (if using).