In a saucepan saute the onions, celery and 1/2 tsp salt in 1 tbsp oil until soft, about 5 minutes.Note: Make sure you use a pot that has a tight fitting lid to cook the rice correctly.
Stir in the 1 cup rice and pour in the 2 cups chicken broth. Bring the pot to a boil.
Reduce the heat to low and cover. Cook according to package instructions.
While the rice cooks whisk together the greek yogurt, mayonnaise, milk, cheese, and garlic powder. Set aside.
Fluff the rice with a fork. Optional: Stir in the chopped mushrooms and chopped water chestnuts.
Pour the cheese sauce over the rice and stir to coat. The rice should be hot enough to melt the cheese.
Serve as a delicious side dish!