Spray a 6‑quart crock pot liner with nonstick spray. Place the 2 pounds boneless skinless chicken breasts in the crock pot.
Pour the 16 ounces Italian dressing evenly over the chicken.
Sprinkle 1/4 cup of the 1/2 cup grated Parmesan cheese and the 1/2 teaspoon ground black pepper over the chicken.
Place the 8 ounces cubed cream cheese on top of the chicken in an even layer. Cover with the crock pot lid.
Cook on high for 4 hours or on low for 5–6 hours.
When the crock pot cooking time is almost done, cook the 16 ounces penne pasta according to package directions; drain and set aside.
When cooking is finished, remove the chicken breasts from the crock pot and shred them with two forks. Return the shredded chicken to the crock pot and stir until the cream cheese is fully incorporated and the sauce is smooth.
Add the cooked penne to the crock pot, stir to combine, then sprinkle the remaining 1/4 cup grated Parmesan cheese over the pasta and stir again.
Garnish with parsley if desired and serve immediately.