Preheat your oven to 375 degrees Fahrenheit. Lightly grease a 9×13 inch baking dish.
Cook the fettuccine according to package directions until al dente. Drain the pasta and set it aside.
While the pasta cooks, heat the olive oil in a large skillet over medium heat. Season the chicken pieces with 1/2 teaspoon salt and 1/4 teaspoon pepper.
Add the chicken to the skillet and cook until browned and cooked through, about 5 to 7 minutes. Add the minced garlic and cook for 1 minute more until fragrant. Remove the skillet from the heat.
In a medium bowl, whisk together the Alfredo sauce, heavy cream, Parmesan cheese, remaining 1/2 teaspoon salt, 1/4 teaspoon pepper, and nutmeg until combined.
Add the cooked pasta and the cooked chicken mixture to the bowl with the sauce. Stir gently until everything is evenly coated.
Stir in 1 1/2 cups of the shredded mozzarella cheese into the pasta mixture.
Pour the entire mixture into the prepared baking dish. Sprinkle the remaining 1/2 cup of mozzarella cheese over the top. If using, sprinkle the breadcrumbs evenly over the cheese layer.
Bake for 20 to 25 minutes, or until the sauce is bubbly and the cheese topping is melted and lightly golden brown.
Let the bake rest for 5 minutes before serving.
Notes
For extra browning, place the dish under the broiler for the last 1-2 minutes, watching closely to prevent burning.
You can substitute cooked rotisserie chicken for the fresh chicken breasts to save time.
Use any short pasta shape like penne or rotini if fettuccine is unavailable.
To make this dish richer, use a blend of Gruyere and mozzarella for the topping.