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 across the top.
04 - Cover and cook on low heat for 4 hours until chicken is thoroughly cooked and tender.
05 - Transfer chicken breasts to a clean surface and shred using two forks. Return shredded meat to the slow cooker.
06 - Stir uncooked fettuccine into the sauce, submerging pasta as completely as possible.
07 - Sprinkle freshly grated Parmesan cheese over the mixture and stir until well combined.
08 - Cover and cook on high heat for 25-35 minutes, stirring once or twice, until pasta reaches al dente texture and sauce achieves desired creaminess.
09 - Serve immediately while hot, topped with chopped fresh parsley.