Steam the broccoli florets until they are just tender. Place the steamed broccoli in the prepared baking dish.
Season the cubed chicken with salt, pepper, garlic powder, and onion powder. Cook the seasoned chicken in a large skillet over medium-high heat until it is no longer pink. Drain off any excess liquid and place the cooked chicken in the baking dish with the broccoli.
In a mixing bowl, combine the cream cheese, sour cream, mayonnaise, Parmesan cheese, and shredded cheddar cheese. Mix until well combined.
Pour the cheese mixture over the chicken and broccoli in the baking dish. Spread it evenly.
Bake the casserole for 25-30 minutes or until it is hot and bubbly and the cheese is melted and golden brown.
Serve hot and enjoy your delicious low-carb Chicken and Broccoli Cheesy Casserole!