Season the chicken breasts with salt, pepper, garlic powder, and Italian seasoning.
In a large skillet, heat olive oil over medium-high heat. Sear the chicken breasts for 3-4 minutes on each side until golden brown. Transfer to the slow cooker.
In a bowl, whisk together chicken broth, heavy cream, Parmesan cheese, and minced garlic. Pour the mixture over the chicken in the slow cooker.
Cover and cook on low for 4-5 hours or on high for 2-3 hours, until the chicken is cooked through and tender.
About 30 minutes before serving, stir in the fresh spinach and cover again to allow it to wilt.
Serve the chicken with the creamy sauce over pasta, rice, or mashed potatoes, and garnish with fresh parsley if desired.