In a large mixing bowl, toss together eggplant, peppers, onion, olive oil herb mix, salt and pepper. Place large piece of aluminum foil (make sure foil extends several inches longer than baking sheet) on baking sheet and spray lightly with cooking spray. Spread vegetables on foil. Cover with another piece of foil, folding bottom foil over top to seal packet. Cut several slits in top of foil pack. Place on grill (I slide the packet onto the grill from the baking sheet). Place tomatoes on top of grill; cover grill; grill tomatoes about 10 minutes, until skin blisters; turn over and grill another 5 minutes; remove from grill. Grill foil wrapped vegetables until tender, about 25 minutes in total.