Add the chicken breasts to the slow cooker. Sprinkle them with salt, pepper, and Italian seasoning.
Place the minced garlic, sun dried tomatoes, and chicken broth around the chicken. Cover and cook on low for 5 to 6 hours.
About 30 minutes before the chicken is done, prepare the polenta. Bring the water to a boil in a medium saucepan. Slowly whisk in the polenta. Reduce heat to low and cook for 20 minutes, stirring often.
Stir the butter, rosemary, and thyme into the polenta. Keep the polenta warm on low heat while you finish the chicken.
Remove the chicken from the slow cooker and shred or slice it. Stir the heavy cream and Parmesan cheese into the slow cooker sauce. Add the fresh spinach and let it wilt for 5 minutes.
Return the chicken to the sauce and stir to coat. Spoon the herbed polenta into bowls and top with the creamy Tuscan chicken and sauce.