Preheat the oven to 350°F (175°C).
Cook the fettuccine pasta according to package instructions until al dente, then drain.
In a large saucepan, combine heavy cream, garlic, and Italian seasoning over medium heat.
Add in the grated Parmesan cheese, stirring until melted and smooth.
In a large mixing bowl, combine the cooked chicken, broccoli florets, and pasta.
Pour the Alfredo sauce over the chicken, broccoli, and pasta mixture, and stir to combine.
Transfer the mixture to a greased baking dish and spread evenly.
Sprinkle breadcrumbs evenly over the top of the casserole.
Bake for 25-30 minutes or until the top is golden brown and bubbling.
Let the casserole cool for 5-10 minutes before serving.