Take a deep bottomed pan, add oil and heat. Splutter mustard seeds. Add the remaining cup of onion pieces and fry till the pieces are dark brown in color.
Add the prawns, red chilly powder and coconut slices. Stir fry until oil shows up.
Add the brinjal pieces and the spicy paste and sufficient salt. Mix well and fry for a couple of minutes.
Add two cups of water and simmer in medium flame till the contents are cooked well.