Bake the eggplant quickly on the embers or on the plate until it softens (turn on all sides). While they are still hot, clean them of the blackened skin. In a bowl, salt and beat with a wooden spoon, putting a little oil, little by little. Finally add very finely chopped onion (it can be made without onions for people who can not stand it). At the end we put mayonnaise and mix well. Serve with tomatoes, cut into slices.