Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, steamed broccoli, cooked rice, cheddar cheese, cream of chicken soup, milk, garlic powder, onion powder, black pepper, and salt. Mix well until all ingredients are evenly coated.
Transfer the mixture to a greased 9x13 inch baking dish, spreading it evenly.
If using breadcrumbs, mix them with olive oil in a small bowl until they are coated. Sprinkle the breadcrumb mixture evenly over the casserole.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.
Remove from the oven and let it cool for a few minutes before serving.