01 - Pat the chicken breasts dry and season both sides generously with salt, freshly ground black pepper, paprika, and dried Italian herbs.
02 - Scatter the finely chopped onion, minced garlic, and sliced sun-dried tomatoes across the bottom of the slow cooker insert.
03 - Lay the seasoned chicken breasts on top of the vegetable mixture in an even layer.
04 - Pour the chicken broth and heavy cream over the chicken breasts. Dot the surface with pieces of unsalted butter.
05 - Cover the slow cooker and cook on the low setting for 4 to 6 hours, or until the chicken is tender and reaches an internal temperature of 165°F.
06 - About 20 minutes before serving, add the packed baby spinach and grated Parmesan cheese to the slow cooker. Stir gently to wilt the spinach and blend the cheese into the creamy sauce.
07 - Taste the sauce and adjust the salt and pepper as needed.
08 - Transfer the chicken breasts to serving plates and spoon the creamy Tuscan sauce generously over the top.