Heat oil in a deep, heavy-bottomed pan over medium heat. Add the curry leaves and sauté until their aroma fills the air. Toss in the finely chopped onions and cook, stirring occasionally, until golden and caramelized.

Mix in the ginger and garlic paste, letting it cook for 1-2 minutes until fragrant. Add the slit green chilies and stir to evenly combine.

Sprinkle the turmeric powder, red chili powder, coriander powder, and cumin powder over the mixture. Stir continuously for about 30 seconds, allowing the spices to bloom and release their oils.

Stir in the chopped tomatoes, pressing them gently with the back of a spoon to help them break down. Cook until the tomatoes are soft, and you notice the oil separating from the spice mixture.

Pour in the coconut milk and water, whisking gently to blend everything into a rich and smooth curry base. Let it simmer for about 5 minutes, allowing the flavors to meld harmoniously.

Add the prawns to the bubbling curry, ensuring they are fully submerged. Cook for 5-7 minutes, or until the prawns turn pink and are tender yet firm to the bite.

Finish with a sprinkle of garam masala for a warm, earthy flavor boost. Adjust the salt according to your taste, stir well, and cook for an additional 2 minutes.

Garnish the curry with a generous handful of freshly chopped cilantro. Serve immediately with hot steamed rice or soft naan bread for a hearty, flavorful meal.