1.Bring A Large Pot Of Lightly Salted Water To A Boil. Add Pasta And Cook For 8 To 10 Minutes Or Until Al Dente; Drain. 2.Melt Butter In A Large Skillet Over Medium Heat. Cook Chicken Until No Longer Pink, And Juices Run Clear. Transfer Chicken To A Cutting Board, And Thinly Slice; Set Aside. Saute Onion Until Tender And Translucent. Add Mushrooms, And Gradually Stir In Cream. Cook, Stirring Constantly, For 7 To 10 Minutes, Or Until Sauce Is Thickened. Stir In Chicken, And Season With Salt And Pepper. Cook 5 Minutes, Or Until Heated Through. Toss With Cooked Pasta Until Evenly Coated.