2.Rub tomatoes with oil, place in roasting pan; roast about 30 minutes or until soft but not coloured.
3.Blend or process garlic, ginger, chillies and seeds until chopped and well combined. Transfer mixture to large heavy-based saucepan; add tomatoes, vinegar, sauce, sugar and turmeric. Simmer about 2 hours or until thick and jammy.
4.Blend mixture, in batches, until chopped coarsely; stir in coriander. Spoon into hot sterilised jars; seal while still hot.
Fish sauce, also called nam pla or nuoc nam, is made from pulverised salted fermented fish, most often anchovies. It has a pungent smell and strong taste, so use sparingly. Available from supermarkets and Asian food stores. Ground cumin is also known as zeera or comino; it has a spicy, nutty flavour and is available from supermarkets.