Brown turkey sausage in a skillet over med-high heat. Drain any grease once it's cooked. Add to slow cooker.
Add in the carrots, beans (SEE NOTES), chicken stock, onions, garlic powder, Italian seasoning, and frozen pearl onions to the slow cooker.
Cover and cook on high for 4-5 hours, depending on how your slow cooker cooks. Check at the 4 hour mark to see if the beans are soft, if not, continue to cook another hour, or until beans are soft.
Once the beans are cooked through, remove lid and discard the bay leaves. Add in the can of fire-roasted tomatoes and stir. (SEE NOTES) The tomatoes are added at the end of the cooking time if you are using dried beans. Dried beans cannot be cooked with acidic foods, like tomatoes or the beans will take much longer to cook to become soft.
Place a few fresh spinach leaves in bowls, and pour soup over. The heat from the soup will wilt the spinach perfectly.