Next time you are invited to a pot luck dinner impress your friends with this attractive yet economical casserole. Mix together puree, yogurt, green chiles, chili powder, coriander, garlic and onion powder. Place tortillas on a rack in a 180ºC oven. Heat until crisp about 5 to 7 minutes. Arrange tortillas in a shallow baking dish. Layer chicken and sauce over tortillas. Bake in 180ºC oven for 25-30 minutes. Serve hot. Garnish with grated sapsago cheese, if desired. This casserole may be frozen before baking. To serve, defrost and follow directions.