Pierce the eggplants in several places with a toothpick. Wrap the whole eggplant in aluminum foil, and set it over a gas grill to cook on all sides until it collapses and begins to release a great deal of steam.
Place the eggplant in a basin of cold water; peel while it's still hot and allow it to drain in a colander until cool.
Squeeze pulp to remove any bitter juices. Mash the eggplant to a puree.
In a food processor, mix the tahini with the garlic, onion, tomato, and lemon juice until the mixture thickens and reduces in size. Thin with water. With the machine running, add the eggplant and the salt, pepper, and olive oil.
Spread out in a shallow dish, and garnish with pepper, parsley, and tomatoes.