Quarter and seed tomatoes. Cut tomatoes into 1/4-inch dice and transfer
to a bowl. Wearing rubber gloves, seed and finely chop chiles.
Finely chop enough onion to measure 1/4 cup and chop cilantro. Stir
chiles, onion, cilantro, and garlic into tomatoes with sugar and lime
juice and salt and pepper to taste. Salsa may be made 1 hour ahead and kept at cool room temperature.