Heat water in a large pot for the pasta and prepare according to package directions.
Heat a large skillet on medium and add oil to the pan.
Once heated, add the diced chicken to the pan. Stir every 20-30 seconds and allow it to cook for 8-10 minutes until cooked through to 165°F. Covering it will also help it cooker faster. Adjust heat as needed.
Add the flour to the pan with the cooked chicken and stir well until it begins to lightly toast, about 3 minutes.
Slowly add the chicken broth, milk, and garlic powder to the pan.
Whisk well to break up lumps and allow the liquid to come to a simmer. The mixture will begin to thicken as it simmers after 2-3 minutes.
If using frozen broccoli, place in a strainer and rinse under lukewarm water to thaw (or microwave for 2 minutes). Drain the water and add to the pan. Fresh chopped broccoli can be added directly into the pan. Stir frequently for 2-3 minutes.
Add the mozzarella and parmesan cheese and stir until melted.
Mix sauce with the cooked pasta, pepper to taste and serve.