In A Saucepan, Saute Onion In Butter Until Tender. Stir In Chicken, Chilies And Mushrooms. In A Small Bowl, Combine Soup, Sour Cream And Hot Pepper Sauce; Add To Pan. Cook And Stir For 5 Minutes. Sprinkle Mozzarella Cheese In The Bottom Of Pie Shell; Add Chicken Mixture. Sprinkle With Cheddar Cheese. Bake At 350 Degrees F For 25-30 Minutes Or Until Filling Is Bubbly And Cheese Is Melted.