Clean, Peel and de-vein the prawns. Add in the salt and turmeric and mix well. Set it on a strainer for the excess water in the prawns to drain. Let it marinate for 30 minutes.
Heat quarter cup of oil in a pan and add in the prawns and the red chilli powder. Fry on low flame for 5 minutes until cooked. Remove from heat and set aside.
Add the remaining quarter cup of oil in the pan and add in the crushed ginger and garlic mixture. Saute for two minutes.
Add in the chopped green chillies and continue to saute until the garlic and the ginger are nicely roasted. About 5 minutes on medium flame.
Add in the masala powders and the salt and fry for a minute.
Add in the prawns, vinegar and quarter cup of water. Do not add all of the vinegar at once. First add the ¼ cup of vinegar and taste it. Add more if you think you might need more. Let it simmer for 5 minutes.
After 5 minutes, the mixture would become slightly dry and the oil would start to float on top completely. Switch off the flame and allow it to cool for an hour.
Transfer the mixture to a ceramic or a glass jar. You can store it refrigerated for upto a month.