Combine: Place chicken breasts in the slow cooker. Season with garlic powder, Italian seasoning, salt, and pepper. Pour in the broth (or water). Cook: Cover and cook on Low for 3-4 hours or High for 2-3 hours. Regular breasts hold up well in the slow cooker, just check that they reach 165°F.
Finish: About 15 minutes before serving, remove the lid. Stir in the heavy cream, parmesan cheese, and spinach.
Melt: Cover and cook for another 10-15 minutes until the spinach is wilted and the sauce is warmed through. Serve over rice, pasta, or potatoes.