Season and cook the chicken:
Heat the olive oil or butter in a large skillet over medium-high heat. Add the chicken pieces and season with salt, pepper, garlic powder, onion powder, and paprika. Cook for 5–7 minutes, or until chicken is browned and cooked through. Remove from skillet and set aside.
Cook the broccoli:
In the same skillet, add the broccoli and a splash of water. Cover with a lid and steam for 3–4 minutes, or until just tender. Remove the lid and let any remaining water evaporate.
Make the cheese sauce:
Push the broccoli to the sides of the pan or remove temporarily. Sprinkle flour into the pan and whisk in the chicken broth and milk. Simmer over medium heat, stirring frequently, until the mixture begins to thicken (about 3–5 minutes).
Add the cheese:
Reduce heat to low and stir in the cheddar cheese and Parmesan, if using. Continue stirring until the cheese has melted and the sauce is smooth.
Combine everything:
Return the cooked chicken to the skillet and stir to coat in the cheese sauce. Mix in the broccoli and combine well. Simmer for another 2–3 minutes until everything is hot and well blended. Taste and adjust seasoning as needed.
Optional baking step:
If desired, transfer everything to a greased baking dish, top with extra shredded cheddar, and broil for 2–3 minutes until golden and bubbly.
Serve:
Serve hot on its own, or over rice, pasta, or mashed potatoes for a full meal.