In a slow cooker, combine broth, tomatoes, beans, carrots, celery, onion, thyme, sage, bay leaves, and 1/2 teaspoon each salt and black pepper. Cover and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours.
Thirty minutes before the soup is done cooking, add ditalini, zucchini and spinach. Cover and cook 30 more minutes. Remove bay leaves and season, to taste, with salt and black pepper. Ladle soup into bowls and sprinkle parmesan cheese over top. Garnish with basil, if desired.