1.Turn On Broiler, And Adjust Rack So It Is As Close To Heat Source As Possible. 2.In A Medium-Size Mixing Bowl, Mix Together Garlic, Olive Oil, Thyme, Vinegar, Salt And Pepper. 3.Put The Mushroom Caps, Bottom Side Up, In A Shallow Baking Pan. Brush The Caps With 1/2 The Dressing. Put The Caps Under The Broiler, And Cook For 5 Minutes. 4.Turn The Caps, And Brush With The Remaining Dressing. Broil 4 Minutes. Toast The Buns Lightly . 5.In A Small Bowl, Mix Capers And Mayonnaise. Spread Mayonnaise Mixture On The Buns, Top With Mushroom Caps, Tomato And Lettuce.