Preheat oven to 400°F and lightly grease a 9×13 baking dish.
Pour the chicken broth, heavy cream, and melted butter directly into the baking dish. Add the garlic powder, salt, pepper, Italian seasoning, onion powder, and parmesan cheese. Whisk everything together right in the dish until well combined.
Stir in the uncooked pasta and make sure all the noodles are coated in the sauce.
Stir in the diced chicken and frozen broccoli florets. Gently press everything down so the pasta is mostly submerged under the liquid.
Cover the dish tightly with foil and bake for 45 minutes.
Remove foil and stir the casserole well. Sprinkle mozzarella evenly over the top.
Return to the oven uncovered and bake 10–15 minutes until the cheese is melted and bubbly.
Allow the casserole to rest for 10 minutes before serving. The sauce will thicken as the pasta absorbs the remaining liquid.