1.Preheat Oven To 400 Degrees F (200 Degrees C). 2.Melt Butter In A Small Skillet Over Medium Heat. Saute Mushrooms And Onion Until Tender; Set Aside. Place Bottom Halves Of Bread On A Lined Cookie Sheet. Top Each With 1 To 2 Slices Turkey, Mushroom/Onion Mixture, And 1 To 2 Slices Cheese. 3.Bake In Preheated Oven For About 5 Minutes, Or Until Cheese Is Melted. Remove From Oven And Top Each Sandwich With Olives, Tomato And Lettuce. Place Top Half Of Bread On Each Sandwich And Serve.