Add the chicken breasts, cannellini beans, chicken broth, diced onion, minced garlic, rosemary, and thyme to the slow cooker.
Season with salt and black pepper, then stir gently to combine the ingredients.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the chicken is fully cooked and tender.
Remove the chicken breasts from the slow cooker and shred them with two forks.
Return the shredded chicken to the slow cooker and stir in the spinach until it wilts.
Ladle the soup into bowls and top each serving with grated Parmesan cheese.