Grilled Vegetables on Onion Rolls

Preparation

1. In a bowl whisk together the vinegar and salt and black pepper to taste, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. Brush the bell peppers with some of the dressing, grill them, skin sides down, on a rack set 4 to 6 inches over glowing coals for 10 to 15 minutes, or until the skin is charred, and transfer them to a bowl, discarding the charred skin. Brush the eggplant, the zucchini, and the onion with some of the remaining dressing, grill the vegetables on the rack, turning them, for 10 to 15 minutes, or until they are browned and tender, and transfer them to the bowl. Brush the cut sides of the rolls with the remaining dressing and grill the rolls, cut side down, for 30 seconds, or until they are toasted lightly. (Alternatively, the vegetables and the rolls can be broiled on the rack of a broiler pan about 2 inches from the heat.) Divide the vegetables among the bottom halves of the rolls, top them with the coriander, and cover the sandwiches with the tops of the rolls, pressing them firmly.