Set oven to 350 degrees.
In a medium dutch oven or a large pot, heat the oil over medium heat.
Sauté the onion, celery, and carrots until soft, usually about 10 minutes. Plan for more time if doubling.
Stir in the garlic and cook another minute.
Stir in the chicken and both rices. This is where you will be thankful you chose a large pot and can get it all mixed!
Then stir in the salt, pepper, and garlic salt.
Reduce the heat to low while you prepare the cheese sauce.
To make the cheese sauce:Melt butter in a medium sauce pan over med/high heat.Whisk in the flour and cook the flour for a minute.Add the salt and pepper and whisk.Slowly add in the chicken broth, whisking continuously. Keep whisking as it starts to thicken.When nearly boiling and thick, reduce heat or remove from heat and add in the cheese and stir until melted. Pour the cheese sauce over the chicken and rice mixture and mix in well.
Transfer the mixture to a 9x13 inch baking dish or two smaller dishes.
Top with additional cheese if desired (skip this step if freezing).
Bake for 25-30 minutes at 350 degrees or until the cheese is melted and bubbling
Serve immediately.Makes 8-10 servings