Marinate the sliced tomato and eggplant for at least one hour.Slice the mozzarella.Heat up an outdoor grill, or a stovetop grill to medium heat.Grill the eggplant until soft and has pretty grill marks.Grill the tomato on either side for about two minutes.Stack the eggplant, then the mozzarella, then the tomato.If you like, top with olive oil.