SPREAD EACH PIECE OF BREAD with thin coating of pureed chiles, or more if you like your sandwich really hot. Cover bottom slice with layer of cheese, tomato and onion slices and as much cilantro as you like. Top with second slice of bread and butter it. Place sandwich, butter-side down, in cast-iron skillet. Spread top piece of bread with butter as well and cook sandwich slowly. When golden brown on bottom, turn it over and cook on the other side. Covering pan will help melt cheese by the time bread is crisped and golden. Eat right away with something very cold to drink.