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