1. Heat olive oil in Dutch oven over medium heat. Add cabbage, onion, carrot, celery and thyme, and cook, stirring occasionally, about 15 minutes, or until softened. Add broth, beans, tomatoes, zucchini and potato, plus 1 cup water. Cover, and bring to a boil. Reduce heat, and simmer, covered, about 15 minutes, or until potato is tender. Remove thyme sprigs.
2. Add more water if soup seems too thick. Stir in bread pieces, and simmer 5 minutes, or until soup is thickened. Add salt to taste.
3. Ladle soup into bowls; drizzle each with olive oil, and sprinkle with parsley. Serve.