Heat Oil In Large Nonstick Skillet. Add Onion And Mushrooms And Cook For 5 Minutes Over Medium Heat. Remove Vegetables And Set Aside. Add Chicken To Skillet And Brown For 2 Minutes Per Side. Add Canned Tomatoes To Skillet And Scrape Up Any Browned Bits. Return Vegetables To Skillet. Stir In Oregano, Salt And Pepper. Reduce Heat To Low. Simmer For 10 To 15 Minutes, Stirring Occasionally, Or Until Chicken Is Cooked. Stir In Wacky Mac And Heat Through.