Heat A Skillet Over Medium Heat. Butter One Side Of Each Slice Of Bread. On The Non Buttered Side Of One Slice, Layer The Feta Cheese, Cheddar Cheese, Red Onion And Tomato. Top With The Other Slice Of Bread With The Butter Side Out. Fry The Sandwich Until Golden Brown On Each Side, About 2 Minutes Per Side. The Second Side Always Cooks Faster.