Preheat the oven to 350°F. Spray a 9x13 casserole dish with non-stick cooking spray and set aside.
In a large stockpot or Dutch oven, heat butter over medium until melted.
Add onion powder, garlic powder, salt, pepper, and bouillon to the butter and saute for 1 to 2 minutes.
Whisk in water and the half and half cream.
Dissolve 4 tablespoons cornstarch in 4 tablespoons of water to make a slurry, and then whisk this slurry into the filling mixture in the pot.
Whisk and cook over medium heat until the mixture comes to a simmer and begins to thicken.
Stir in broccoli florets and cook 1 to 2 minutes longer.
Spread cooked noodles and diced chicken evenly in the prepared casserole dish.
Pour the broccoli/sauce mixture over the top and stir to combine everything evenly.
Bake, covered with aluminum foil, for 30 minutes or until broccoli is fork-tender. Remove from the oven.
Stir the casserole to redistribute sauce. Sprinkle with cheese. Place foil loosely over the casserole and leave to set for 5 minutes. For a browned cheese, you can return the casserole, uncovered, to the oven for 5 to 10 minutes instead of setting it for 5 minutes.