Grill or roast the eggplants until skin dark/carbonized and really tender all over. Cut them open, scoop the content and place it in the colander to drain the excess water for about 30 min.
Chop them well with a knife until fairly smooth. Transfer into a bowl, season with salt (to taste) and pour in the oil mixing continuously. Finely chop the onion and mix it in, blending everything well. (Or give them a pulse or two in the food processor along with the salt, oil and onion. Carefully, not to make it too smooth.)
Serve this dip spreading it over toasted bread, topped with tomato and bell peppers slices. Or the vegan way, dip in with carrots, cucumber, celery sticks.