Preheat your oven to 190°C (375°F). Lightly grease a 2-liter (2-quart) casserole dish with cooking spray or butter.

Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the chopped chicken pieces and cook until lightly browned on all sides, about 5-7 minutes. Remove the chicken from the skillet and set aside.

Add the chopped onion to the same skillet and cook until softened and translucent, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant.

Add the uncooked rice to the skillet with the onions and garlic. Stir for about 1 minute to lightly toast the rice.

Pour in the chicken broth and milk. Stir in the cream of chicken soup, salt, and pepper until well combined and smooth. Bring the mixture to a simmer, stirring constantly.

Stir in the cooked chicken and the frozen mixed vegetables. Ensure everything is evenly distributed throughout the creamy sauce.

Pour the entire mixture into the prepared casserole dish. Spread it evenly.

If using cheese, sprinkle the shredded cheddar cheese evenly over the top of the casserole.

Cover the casserole dish tightly with aluminum foil. Bake in the preheated oven for 40 minutes.

Remove the aluminum foil and bake for an additional 10-15 minutes, or until the rice is fully cooked, the sauce is bubbly, and the cheese (if used) is melted and lightly golden.

Let the casserole rest for 5-10 minutes before serving. Garnish with fresh chopped parsley, if desired.