Heat Oil In A Large Skillet Over Medium Heat. Add Chicken, And Saute Until Browned, About 5 To 7 Minutes. When Chicken Is Browned, Stir In Sour Cream, Mushrooms, Ketchup And Mustard; Season With Garlic Powder, Salt And Pepper. Reduce Heat To Low. Simmer For About 20 Minutes, Or Until Chicken Is No Longer Pink And Juices Run Clear.