in blender put oil, tomatoes, tomato puree, chilli powder, corriander powder, garlic, salt and 1 cup of water and blend to a paste.
pour in pot, add half cup of water n keep on flame let it boil properly if it thickens can add water, when its olmost cooked add prawns if u want can add potatoes cubes with skin, raw mango and spring onions cook till prawns are done
garnish with green chillies and corriander powder....
NB: this recipe is also same as fish or dry fish curry