Toast the chiles in a dry skillet or saucepan over medium-low heat, shaking the pan, about 2 minutes. Pour 1/2 cup boiling water on top, cover and let soak 15 minutes.
Meanwhile, preheat a grill or grill pan to high. Grill the tomatoes, turning, until charred. Transfer to a food processor. Add the chiles and their soaking water, onion, garlic, oregano, lime juice, sugar and 1 1/4 teaspoons salt; pulse until chunky. Set aside, about 1 hour. Garnish with cilantro.
Photograph by Tina Rupp
Courtesy of Aaron Sanchez for Food Network Magazine