Grind coconut, coriander powder, chili powder, turmeric powder, and fennel seeds into a fine paste with little water.
In a pot, add tomatoes, green chilies, crushed ginger-garlic, curry leaves, coconut paste, salt, and water. Mix and cook until the raw smell leaves.
Add prawns and Malabar tamarind. Cook for 5 minutes.
Heat coconut oil, fry red chilies, sliced onions, curry leaves, and salt until onions turn reddish. Add this tempering to the curry.
Let the curry rest for a few hours for enhanced flavor. Serve with rice or roti.