Preheat oven to 350ºF. Spray a 9×13-inch baking dish with nonstick cooking spray.
Bring a large pot of water to a boil over medium-high heat. Add spaghetti noodles and cook spaghetti according to the package directions for al dente. Drain and set aside.
Stir together softened butter and cream cheese in a large bowl. Add cream of chicken soup, shredded chicken, cooked pasta, garlic cloves, Italian dressing mix, ½ cup shredded cheese, and chicken stock to the bowl and stir to combine.
Pour the pasta mixture into the prepared casserole dish. Top with remaining 1½ cups shredded cheese.
Cover the pan with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 to 20 minutes or until bubbly and the cheese is melted.
Garnish with fresh parsley.
