Soak chillies in hot water until soft, about 30 minutes. Drain, but reserve water. Blend chillies, garlic, ginger, turmeric and mustard seeds to a paste with a little chilli water in a food processor.
Slice eggplants into 1 cm thick rounds. Heat oil in a frying pan, then add spice paste and stir for a few minutes to release flavours. Add eggplant and cook until soft, stirring occasional