Preheat a non-stick wok or frying pan. Dry-fry the onion and garlic until soft and lightly coloured. Add the aubergine and mushrooms, browning for 4-5 minutes.
Transfer to a slow cooker and add the remaining ingredients. Simmer on a low setting for 2 hrs. Reduce the heat and allow to simmer gently as the sauce thickens.
Just before serving stir in the basil.