Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish. Cook penne pasta according to package directions for al dente. Drain and set aside.

While pasta cooks, season chicken pieces with salt, pepper, and Italian seasoning. Heat olive oil in a large skillet over medium-high heat. Add chicken and cook until golden brown and cooked through, about 5-7 minutes. Remove chicken from the skillet and set aside.

In the same skillet, melt butter over medium heat. Add minced garlic and cook until fragrant, about 30 seconds. Whisk in the flour and cook for 1 minute, stirring constantly.

Gradually whisk in the heavy cream and milk until smooth. Bring to a simmer and cook for 3-5 minutes, stirring occasionally, until the sauce has thickened.

Remove the skillet from the heat. Stir in the freshly grated Parmesan cheese and nutmeg until the cheese is melted and the sauce is smooth. Season with additional salt and pepper to taste.

In a large bowl, combine the cooked pasta, cooked chicken, and the alfredo sauce. Mix well to ensure everything is evenly coated.

Pour the mixture into the prepared baking dish. Sprinkle the shredded mozzarella cheese evenly over the top.

Bake for 20-25 minutes, or until the sauce is bubbly and the topping is golden brown. Let it rest for 5-10 minutes before serving.