Season the chicken breasts with salt and black pepper on both sides. Heat olive oil in a skillet over medium-high heat and sear the chicken for 3-4 minutes on each side until golden brown. Remove and set aside.
In the same skillet, sauté minced garlic for 30 seconds until fragrant. Add chicken broth and bring to a simmer, scraping up browned bits from the skillet.
Reduce heat to low, stir in heavy cream, Parmesan cheese, and dried Italian herbs. Mix until cheese melts and sauce is smooth.
Return the chicken to the skillet, ensuring it is coated with the sauce. If using, add fresh spinach and let it wilt.
Transfer the mixture to a slow cooker. Cook on low for 4-6 hours or on high for 2-3 hours until chicken is tender.
Serve hot, garnished with fresh parsley.