Preheat your oven to 350°F.
In a large mixing bowl, combine the shredded chicken, steamed broccoli, cooked rice, cheddar cheese, cream of chicken soup, milk, garlic powder, onion powder, salt, and pepper. Mix well until all ingredients are evenly coated.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it out evenly. If using breadcrumbs, mix them with olive oil and sprinkle over the top of the casserole for added crunch.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.
Let the casserole cool for about 5 minutes before serving to allow it to set for easier slicing.