Roast chiles, turning frequently with tongs, until skins are blistered and lightly charred all over, 4 to 6 minutes (6 to 8 minutes if broiling). Transfer chiles immediately to a large bowl, then cover with plastic wrap. Let stand 20 minutes, then peel or rub off skin. Discard seeds, ribs, and stems from chiles, then cut into 1-inch pieces.