Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the cooked rice, broccoli florets, shredded cheddar cheese, shredded mozzarella cheese, cream of mushroom soup, milk, garlic powder, onion powder, salt, and pepper. Mix well until all ingredients are evenly combined.
Pour the mixture into a greased 9x13 inch baking dish, spreading it evenly.
If desired, mix the breadcrumbs with olive oil and sprinkle over the top for a crunchy topping.
Cover the baking dish with aluminum foil and bake for 25 minutes.
After 25 minutes, remove the foil and bake for an additional 20 minutes, or until the casserole is bubbly and the top is golden brown.
Once done, remove from the oven and let it rest for 5-10 minutes before serving.