Preheat your oven to 375°F and lightly grease a 9x13 baking dish.
Cook the pasta just until al dente. Drain and set aside.
In a large skillet, melt butter over medium heat. Stir in flour and whisk for one minute.
Slowly whisk in the milk and chicken broth until smooth. Let it thicken for 3-4 minutes.
Stir in garlic powder, onion powder, salt, pepper, and 1 1/2 cups of cheese until melted.
Add the pasta, chicken, and broccoli into the sauce. Stir until well combined.
Transfer everything into the baking dish. Top with remaining cheese.
If using breadcrumbs, mix them with olive oil and sprinkle on top.
Bake uncovered for 20-25 minutes until bubbly and golden on top.
Let it rest for a few minutes before serving — it’s molten hot straight from the oven.