Split aubergine in half(leave stalk on to be pretty). Slash crosscuts in flesh not quite as far as skin. Put into baking dish - tight as poss, then put on thin slices of onions and quartered cherry tomatoes. Cover in olive oil. Roast very slowly - an hour at least - so the tomatoes and onions melt into the flesh. Add more oil if necessary. Best eaten cold - poss sprinkled with fresh coriander. Yum
Oh, and just roast them in a tray with mushrooms, courgettes, peppers, sweet potatoes etc - dressed with a bit of oil (garlic olive oil's good). Yummy on their own, and also to use as a base for a ratatouille.
They are great in curry as they absorb the spice flavours beautifully.
There is also a Greek dish called melitsanosalata (aubergine salad) which sometimes you find with the hummus and taramasalata. Haven't made it for ages but I suspect it involves roasting the aubergines then whizzing them in the food processor with olive oil, garlic and breadcrumbs, so similar.