Preheat your oven to 350°F (175°C).
In a large bowl, combine the cooked chicken and broccoli.
In another bowl, mix the cream of chicken soup, milk, garlic powder, salt, and pepper.
Add the soup mixture to the chicken and broccoli, stirring until well combined.
Transfer the mixture to a greased 9x13 inch baking dish.
Sprinkle the shredded cheddar cheese evenly over the top.
If using, mix breadcrumbs with a little melted butter and sprinkle over the cheese.
Bake in the preheated oven for 30 minutes or until bubbly.
Let the casserole cool for a few minutes before serving.
Garnish with fresh herbs if desired and enjoy!