Prepare a grill for medium heat.
Put the tomatoes, zucchini, eggplant and onion on the grill and cover. Grill the tomatoes, turning occasionally, until lightly charred, 5 to 6 minutes. Grill the zucchini, eggplant and onion, turning every 5 minutes, until lightly charred and tender when poked with the tip of a small, sharp knife, 15 to 20 minutes.
When cool enough to handle, chop all of the vegetables except the onion into bite-size pieces and add to a medium bowl. Chop the onion finely and add to the bowl. Fold in the oil, basil, parsley, thyme, garlic and 1 tablespoon salt. Serve warm or at room temperature.