Prick eggplants with a fork. In a very hot oven (450 degrees) or under a broiler, roast the eggplants for 30 to 45 minutes, or until their skins are blackened and their insides are extremely soft. Let cool, then scoop the flesh into a colander. Press gently so that the juices drain away.
Put the eggplant flesh in a bowl and mash with a fork or a potato masher. Add the olive oil and yogurt and continue mashing and blending. Add the lemon and garlic, if using, and salt to taste. Mix in the parsley or mint, if using. Taste again. Serve.