Spray a large saucepan or soup pot with nonstick cooking spray. Add the onion, carrot and celery and cook over low heat, stirring often until the vegetables have softened.
Add the garlic and stir for another minute.
Add the broth, tomatoes, cabbage, spinach, tomato paste, basil, thyme and salt and bring to a boil over medium high heat. Lower the heat, cover the pot and simmer gently for about 15 minutes.
Add the zucchini and cook until softened, 3 – 5 minutes more.
Stir in chopped fresh parsley or basil just before serving if desired.
Slow Cooker Instructions
Place everything in your slow cooker, cover and cook on LOW until tender, 6 to 8 hours.