Preheat your oven to 350 degrees F. If using raw chicken breast (not pre-cooked), place chicken on a sheet pan and bake for 25 minutes. Remove from oven and let cool for 10 minutes before shredding. Bump the oven temperature to 400 degrees F to prepare for the casserole.
While chicken is cooking, make the rice (if not using pre-cooked rice). Boil your rice in a pot of 6 cups of water. After 8 minutes, drain the water. This method is much easier and resembles cooking rice like pasta!
Now make the cream of mushroom sauce. Heat a large saucepan to medium heat. Once hot, add the butter or oil, then the onion, mushrooms, and garlic. Sauté for 5-7 minutes, or until softened and golden. Sprinkle the mixture with flour and cook another minute.
Now add the wine, followed by the milk. Increase the heat to medium high until the sauce begins to thicken, then lower the temperature to medium low. Slowly stir in about 1/2 cup of the parmesan cheese and let melt.
Lightly grease a 9x13 sized casserole dish. Place the cooked rice and shredded chicken in the pan. Top with the cream of mushroom sauce and give it a good stir. Top with parmesan cheese and transfer to the oven.
Bake at 400 degrees F for about 20 minutes, or until the parmesan is lightly browned and crispy. Remove from oven and serve hot!