01 - Arrange chicken breasts at the bottom of the slow cooker. Season evenly with salt, pepper, and Italian herbs, ensuring all pieces are coated.
02 - Scatter chopped onion and minced garlic evenly 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 heat for 4 hours, or until chicken reaches an internal temperature of 165°F and is fork-tender.
05 - Transfer cooked chicken to a cutting board. Using two forks, shred into bite-sized pieces. Return shredded chicken to the slow cooker.
06 - Stir in uncooked fettuccine, submerging noodles completely in the liquid as much as possible.
07 - Sprinkle freshly grated Parmesan cheese over the mixture. Stir thoroughly to distribute evenly throughout the sauce.
08 - Cover and cook on high heat for 25-35 minutes, stirring once or twice during cooking, until pasta is al dente and sauce has thickened to a creamy consistency.
09 - Ladle hot pasta into bowls and garnish with chopped fresh parsley before serving.