Preheat the oven to 475 degrees F.
Slice the baby eggplants in half lengthwise, keeping the stalks on; this is an aesthetic consideration, nothing to do with flavor, but humor me.
Pour the 3 tablespoons regular olive oil into a very shallow roasting pan, sprinkle in the dried oregano, add the eggplants, cut-side down, and swirl them gently around. then turn them so they are cut-side up and put the pan in the hot oven for 15 minutes, by which time they should be tender and turning gold in parts.
As soon as the eggplants are in the oven, put the fine half-moons of red onion in a bowl and cover with the red wine vinegar and salt.
Remove the cooked eggplants to a platter, and now whisk into the vinegary onions the extra-virgin olive oil, then grate in (or mince and add) the garlic and, finally, whisk in the cold water.
Pour this over the warm eggplants, using your hands to arrange the glowingly pink onion over them evenly, then leave it all for about half an hour to cool to room temperature before you eat, scattering with fresh oregano, if you have any, when serving.
Reprinted from Nigellissima. Copyright (c) 2012 by Nigella Lawson. Published by Clarkson Potter, a division of Random House LLC. All rights reserved.