01 - Place chicken breasts in the bottom of the slow cooker. Season evenly with salt, black pepper, and dried Italian herbs.
02 - Scatter chopped onion and minced garlic over the seasoned chicken.
03 - Pour chicken broth and heavy cream into the slow cooker. Distribute cream cheese cubes and butter pieces on top.
04 - Cover and cook on low heat for 4 hours, until chicken is fully cooked and tender.
05 - Transfer chicken breasts to a clean surface. Shred using two forks, then return meat to the slow cooker.
06 - Stir uncooked fettuccine into the sauce, pressing down to submerge pasta as much as possible.
07 - Sprinkle 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, until pasta is al dente and sauce has thickened.
09 - Ladle into bowls and garnish with freshly chopped parsley. Serve immediately.