Clean, wash, and drain the prawns. Marinate the prawns with half of turmeric powder, red chilli powder, and salt. Leave it aside for 30 mins.

Meanwhile, heat oil in a claypot. Splutter mustard seeds and curry leaves. Add the chopped shallots, turmeric powder, and salt and saute until translucent. Add the ginger-garlic paste and green chilies. Saute until the raw smell goes away. Add the chopped tomatoes and saute until soft and mushy. Add the remaining spice powders-chilli powder, fenugreek powder, coriander powder, and pepper powder. Fry until the oil starts to separate from the masala.

Add the marinated prawns and fry for 2-3 mins. Add 1/2 cup of water along with the tamarind pulp and bring it to a boil. Reduce the flame and cook until the prawns are done and the sauce thickens. Add the coconut milk, simmer for another 5-10 mins. Check the seasoning and serve with steamed rice, tapioca, or roti.