Preheat oven to 350 degrees F. Butter a large casserole dish and set aside.
Heat olive oil in a large skillet over medium heat. Season both sides of chicken breasts with Italian seasoning, salt, and pepper to taste. Add to pan and cook until the chicken is cooked through, about 4 to 5 minutes per side. Remove chicken and wipe the skillet clean. Let the chicken rest for 5 minutes before slicing crosswise.
In a large bowl, combine cooked pasta, chicken, and alfredo sauce. Spread about half of the pasta mixture on the bottom of the casserole dish then sprinkle with half of the mozzarella. Add the remaining pasta mixture and top with more mozzarella. Bake until bubbly and beginning to brown on top, about 20 minutes. Garnish with parsley and serve immediately.
