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 evenly across the top.
04 - Cover and cook on low setting for 4 hours, or until chicken reaches internal temperature of 165°F and is tender.
05 - Remove cooked chicken breasts from slow cooker. Shred using two forks, then return meat to the pot.
06 - Stir in uncooked fettuccine, submerging noodles completely in the liquid.
07 - Sprinkle grated Parmesan cheese over the mixture and stir thoroughly to combine.
08 - Cover and cook on high for 25 to 35 minutes, stirring occasionally, until pasta is al dente and sauce has thickened.
09 - Ladle into bowls and garnish with fresh chopped parsley.