Place the chicken breasts in the slow cooker. Add the chicken broth, sun-dried tomatoes, garlic, onion, Italian seasoning, salt, and pepper.
Cover and cook on low for 6 hours until the chicken is tender and shreds easily.
Remove the chicken, shred it with two forks, and return it to the slow cooker.
Stir in the heavy cream and fresh spinach. Cover and cook on low for 20 more minutes until the spinach wilts.
Ladle the soup into bowls and top each serving with grated Parmesan cheese.