Kerala Style Prawns Curry

Name: Kerala Style Prawns Curry
Ingredients: For Marination:; 25-30 Fresh Tiger Prawns (Deshelled and Deveined); 1/2 tsp Turmeric Powder; pinch Black Pepper Powder; 1 Lemon; as per requirement Salt to Season; 3 tbsp Coconut Oil; 1 tsp Mustard Seeds; 1/8 tsp Fenugreek Seeds; 1 1/2 Inch Ginger (Finely Chopped); 6 cloves Garlic (Finely Sliced); 5-6 Green Chillies (Chopped into Half); 2 sprigs Curry Leaves; 10-12 Pearl/Sambar Onions (Chopped); 2 tsp Ginger Garlic Paste; 1 tbsp Kashmiri Red Chilli Powder; 1 tbsp Spicy Red Chilli Powder; 2 tbsp Coriander Powder; 1/8 tsp Fenugreek Powder; 2 Fish Tamarind; as required Hot water (As per desired consistency); 1 sprig Curry Leaves (For Garnish)