Bring a large pot of salted water to a rolling boil. Add the penne pasta and cook until al dente, about 11 minutes. Drain well and set aside so it’s ready to be layered later.
In a medium saucepan, melt the butter over medium heat. Add minced garlic and sauté for 30 seconds until fragrant. Stir in the cream cheese and slowly add milk, whisking until smooth. Mix in Parmesan, parsley, Italian seasoning, salt, and pepper. Let it simmer gently for 5 minutes until it thickens.
Heat olive oil in a skillet over medium heat. Season chicken breasts with salt and a little garlic powder. Cook for about 5–6 minutes per side until fully cooked and the internal temperature reaches 165°F. Remove from heat and cut into bite-sized cubes.
Preheat your oven to 375°F. Lightly grease your casserole dish with butter. Layer cooked pasta, chicken, and Alfredo sauce, repeating until all ingredients are used. Finish with a final layer of sauce and a sprinkle of Parmesan on top.
Cover the casserole with aluminum foil and bake for 15 minutes. Remove foil and bake an extra 5 minutes until the cheese is golden and bubbly. Serve hot and enjoy that creamy, cheesy goodness.