Spray the slow cooker insert with non-stick cooking spray.
Season the chicken breasts with Italian seasoning, garlic powder, salt, and black pepper on both sides.
Place the seasoned chicken breasts in the slow cooker.
In a medium bowl, whisk together the heavy cream, chicken broth, grated Parmesan cheese, and minced garlic until combined.
Pour the Alfredo sauce mixture over the chicken breasts in the slow cooker.
Cover and cook on low for 3 to 4 hours, until the chicken is cooked through and tender.
Remove the chicken breasts from the slow cooker and shred them using two forks.
Break the uncooked fettuccine pasta in half and add it to the slow cooker, stirring to submerge the pasta in the sauce.
Return the shredded chicken to the slow cooker and stir to combine.
Add the unsalted butter to the slow cooker and stir until melted and incorporated.
Cover and cook on low for an additional 20 to 30 minutes, stirring occasionally, until the pasta is tender and the sauce has thickened.
Taste and adjust seasoning with salt and pepper if needed.
Serve the Chicken Alfredo garnished with chopped fresh parsley.