Add the chicken to the bottom of a 6-quart slow cooker.
Place the cream cheese, cream of chicken soup, Italian dressing seasoning mix, and butter on top of the chicken. Add garlic powder and black pepper if using.
Cover and cook on LOW for 5–6 hours or on HIGH for 3–4 hours, until the chicken is tender.
Remove the chicken, shred or slice it, then return it to the slow cooker.
Stir the sauce well until smooth and creamy. Add a splash of broth if it’s too thick.
Cook angel hair pasta in salted boiling water, drain, and serve topped with the chicken and sauce.
Garnish with parsley or parmesan if desired.