Roughly chop the prawns into small pieces. Marinate with a little salt and turmeric powder. Keep aside.
Heat 1.5 tbsp oil in a pan, add the ginger, half the chopped onions and 3-4 green chilies. Fry till the onions catch a tinge of golden brown.
Now throw in the prawns, saute till just cooked. Take care to not overcook the prawns. Remove from flame, allow to cool to room temperature.
Keep aside half the cooked prawns in a mixing bowl.
Blitz the other half in an electric blender to a coarse paste.
To the same mixing bowl, now add the coarsely ground prawns, coriander leaves and the remaining onions and green chilies. Give it all a hearty mix. Mash gently with the back of a ladle.
Adjust seasonings. Throw in more green chilies if you like the heat. Finish with a generous drizzle of mustard oil and a squeeze of lemon. Serve with piping hot rice.