Place the eggplants and peppers on a charcoal grill or on a metal rack placed on the stovetop. Roast, turning occasionally, until the skins are charred and separated from the flesh, 4 to 5 minutes on the grill, or 7 to 8 minutes on the stovetop. Place the peppers in a plastic bag and seal for an hour, allowing the steam to further soften them.