Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with olive oil.
In a large mixing bowl, combine the cooked chicken, uncooked rice, cream of chicken soup, chicken broth, frozen mixed vegetables, garlic powder, onion powder, black pepper, and salt. Stir until well combined.
Pour the mixture into the prepared baking dish and spread it out evenly.
Cover the dish tightly with aluminum foil and bake in the preheated oven for 45 minutes.
After 45 minutes, remove the foil and stir the casserole. Pour the milk over the top, then sprinkle the shredded cheddar cheese evenly on top.
Return the casserole to the oven, uncovered, and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for 5 minutes before serving. Garnish with chopped parsley if desired.