Bell peppers, eggplant and zucchini are staples in the Mediterranean garden. Here, they are roasted on a grill, along with sweet corn, until their textures are yielding and the flesh is lightly perfumed with smoke. Combined with classic Italian pesto, the grill-roasted vegetables make a delicious and colorful summer salad. The pesto can be made up to 2 days in advance and stored in a container in the refrigerator with a thin layer of olive oil poured over the top. If you like, make a double batch of the pesto, which can be tossed with pasta or served with grilled chicken or fish.