Preheat your oven to 375°F (190°C) and position the rack in the top third.

In a large pot, bring salted water to a rolling boil. Add uncooked penne pasta and cook for 1 minute less than package directions suggest. Add broccoli florets to the pot and let them cook together for an additional 2 minutes.

Once cooked, drain the pasta and broccoli together in a colander, then transfer the mixture to your prepared casserole dish.

In the casserole dish, mix in cooked chicken, Alfredo sauce, Parmesan cheese, and Italian seasoning. Toss everything until evenly coated.

Spread the mixture evenly across the casserole dish, then sprinkle shredded mozzarella cheese on top.

Place the casserole in the oven and bake uncovered for 15-20 minutes, until the cheese is hot, bubbly, and golden.

Remove from the oven and let sit for a couple of minutes before serving. Taste and adjust with additional salt and pepper if needed.