01 - Place chicken breasts in the bottom of the slow cooker. Season evenly with salt, pepper, and 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 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 and shred using two forks. Return shredded chicken to the slow cooker.
06 - Add uncooked fettuccine to the slow cooker, stirring to submerge pasta completely in the liquid.
07 - Sprinkle grated Parmesan cheese over the mixture and stir well to combine.
08 - Cover and cook on high setting for 25 to 35 minutes, stirring once or twice, until pasta is al dente and sauce has thickened to creamy consistency.
09 - Portion hot Alfredo into bowls and garnish with freshly chopped parsley.