Place the 1.5 lbs of chicken breasts in an even layer at the bottom of the slow cooker.
In a small bowl, whisk together the 0.5 cup chicken broth, 0.5 cup heavy cream, 3 cloves minced garlic, 1 tbsp Italian seasoning, and 0.5 cup chopped sun-dried tomatoes. Pour this mixture evenly over the chicken.
Cover and cook on LOW for 4 hours (or HIGH for 2 hours) until the chicken reaches an internal temperature of 165F and is cooked through.
During the last 15 minutes of cooking, stir in the 2 cups of fresh spinach and 0.5 cup grated Parmesan cheese. Recover and let cook until the spinach wilts completely.
Sprinkle the 1 cup shredded mozzarella cheese evenly over the top of the chicken. Cover for a final 5 minutes until the cheese is completely melted before serving.