In a mixing bowl, combine the cleaned prawns with 1/4 teaspoon turmeric powder, 1/2 teaspoon Kashmiri red chili powder, 1 teaspoon lime juice, and 1/2 teaspoon salt. Toss to coat evenly and let sit at room temperature for 10 minutes.

Heat 2 tablespoons of coconut oil in a deep sauté pan or kadai over medium heat. Once hot, add 1/2 teaspoon of mustard seeds. When they begin to crackle and pop, add the 10 curry leaves and stir quickly for about 10 seconds until fragrant.

Add the finely chopped onion to the pan. Cook over medium heat, stirring occasionally, for 6 to 8 minutes, or until the onions turn soft and translucent with light golden edges. Add 1 tablespoon of ginger-garlic paste and sauté for another minute until the raw smell disappears.

Stir in the chopped tomato, 1 teaspoon Kashmiri red chili powder, 1 tablespoon coriander powder, 1/2 teaspoon cumin powder, 1/4 teaspoon turmeric powder, and 1/2 teaspoon salt. Cook for 4 to 5 minutes, stirring frequently and mashing the tomatoes with your spoon, until they soften completely and the oil starts to separate at the edges.

Turn the heat down to low. Pour in 200 ml of coconut milk, 120 ml of water, and the diluted tamarind paste. Stir thoroughly to combine. Allow the gravy to come to a gentle simmer over medium-low heat for about 3 minutes.

Gently slide the marinated prawns into the simmering curry. Cook over medium-low heat for 3 to 4 minutes, stirring occasionally, until the prawns turn completely opaque, pink, and curl into a loose 'C' shape. Turn off the heat immediately. Garnish with chopped coriander leaves and serve warm.