1.Heat The Butter In A 10-Inch Skillet Over Medium Heat. Add The Onion And Cook Until It'S Tender. 2.Stir In The Soup, Milk And Tomatoes. Heat To A Boil. Add The Fish To The Skillet And Reduce The Heat To Low. Cover And Cook For 10 Minutes Or Until The Fish Flakes Easily When Tested With A Fork. 3.Serve Over Linguine.