Dice the onion and chop the celery and carrots. Mince the garlic.
Put the beans in a colander and rinse well under cold water.
Put the onion, celery, carrots, garlic, bean mix, broth, water, fire-roasted tomatoes, bay leaves, oregano, salt, thyme, red pepper flakes, and pepper into a slow cooker. Stir well and put the lid on. Turn the dial to high and cook for 4 hours or cook on low for 7-8 hours.
Test the beans to make sure they are soft. If so, remove the bay leaves, add the spinach and cook for 15 more minutes.
Optionally garnish the soup with fresh chopped basil and serve.