01 - Place chicken breasts in the bottom of the slow cooker. Season evenly with salt, black pepper, and dried Italian herbs.
02 - Scatter the chopped onion and minced garlic over the seasoned chicken.
03 - Pour in the chicken broth and heavy cream. Distribute the cream cheese cubes and butter evenly across the top.
04 - Cover and cook on low setting for 4 hours, or until chicken reaches an internal temperature of 165°F and is tender.
05 - Transfer cooked chicken breasts to a cutting board. Shred using two forks, then return the meat to the slow cooker.
06 - Stir in the uncooked fettuccine, submerging the noodles as completely as possible in the liquid.
07 - Sprinkle the grated Parmesan cheese over the mixture and stir thoroughly to combine.
08 - Cover and cook on high heat for 25-35 minutes, stirring once or twice during cooking, until pasta is al dente and sauce has thickened to a creamy consistency.
09 - Ladle into bowls and garnish with chopped fresh parsley. Serve immediately.