Marinate the prawns with turmeric powder, chilly powder, paprika, ginger powder, garlic powder, lemon juice, water and salt.
Shallow fry the prawns, until golden in colour and keep aside.
Heat 2 tbsp of oil in a pan.
Add sliced onions and fry, till they become brown.
Add garlic, ginger, green chillies, curry leaves, chopped tamarind, tomato puree and green mango.
Lower the flame.
Add turmeric powder, chilly powder, coriander powder, cumin powder, fenugreek powder, paprika and coconut cream along with water or coconut milk.
Simmer for 20 minutes.
Add prawns.
Place them on a serving dish.
Heat 3 tbsp of oil in a pan.
Fry the onions, till they become dark brown.
Add mustard seeds and when they splutter, add curry leaves.
Add fresh coriander leaves.
Pour the above seasoning into the gravy.