Preheat your oven to 350°F (175°C). Grease a large baking dish.
Cook the pasta according to package instructions until al dente. Drain and set aside.
In a saucepan, melt the butter over medium heat. Stir in the flour until smooth. Gradually add the milk and chicken broth, whisking constantly until the mixture thickens.
Stir in the garlic powder, onion powder, salt, and pepper. Let it simmer for a few minutes until the flavors meld.
In the prepared baking dish, layer half of the cooked pasta, followed by half of the chicken, broccoli, diced tomatoes, and shredded cheese. Pour half of the sauce over the top. Repeat the layers.
Cover the baking dish with aluminum foil and bake for 30 minutes. Then, uncover and bake for an additional 15 minutes until the cheese is bubbly and golden.
Let it cool for a few minutes before serving. Enjoy the cheesy goodness!