Preheat your oven to 350°F (175°C). Grease the 9x13 inch baking dish with a little oil or cooking spray.
In a medium saucepan, combine the cream of chicken soup and milk. Whisk them together over medium heat until smooth and heated through.
In a large mixing bowl, combine the cooked rice, shredded chicken, broccoli florets, garlic powder, onion powder, salt, and pepper. Mix well.
Pour the warm soup mixture over the chicken and rice mixture. Stir until everything is well combined.
Add 1 1/2 cups of the shredded cheddar cheese into the mixture and stir to incorporate.
Pour the entire mixture into the prepared baking dish and spread it evenly.
Top the casserole with the remaining cheddar cheese and, if desired, sprinkle breadcrumbs evenly over the top for added crunch.
Bake in the preheated oven for 30-35 minutes, or until the cheese is bubbly and the top is slightly golden.
Remove from the oven and allow it to cool for a few minutes before serving.