Rinse the dried white beans under cold water and remove any debris.
In the slow cooker, combine the rinsed beans, diced onion, minced garlic, diced carrots, diced celery, undrained diced tomatoes, broth, thyme, rosemary, bay leaf, salt, and pepper.
Stir the ingredients together until well mixed.
Cover the slow cooker and set it to cook on low for 6 to 8 hours or on high for 3 to 4 hours, until the beans are tender.
About 30 minutes before serving, add the chopped kale or spinach, if using. Stir well and let it cook for the remaining time.
Before serving, remove the bay leaf. Adjust the seasoning with more salt and pepper, if needed.
Ladle the soup into bowls and garnish with fresh parsley.