If you want to cook this recipe ahead of time and freeze it, this is what I recommend: Cook the chicken with the rice and onions. Shred and let cool. Place in a freezer-safe air-tight container and freeze. You could also precook the rice and freeze in a separate container. When ready to eat, pull the rice and chicken containers from the freezer and let them thaw overnight in the fridge. Then combine the chicken mixture and rice in a large microwave-safe bowl and reheat in the microwave for about 4 to 5 minutes. Then add the sour cream and cheese, stir, and heat for another minute or two until the cheese is melted. You could also reheat it on the stovetop.