In a glass bowl, combine the prawns with turmeric, lime zest, lime juice, salt, pepper, half of the curry powder, and crushed garlic. Mix well to coat the prawns evenly, then cover and refrigerate for 20 minutes.
Heat olive oil in a large pan over medium-high heat. Add the chopped onions, seeds, cardamom, curry leaves, the remaining curry powder, garlic, ginger, chilies, salt, and pepper. Cook, stirring occasionally, for about 10 minutes until the onions are soft and slightly golden.
Add the chopped tomatoes, tamarind paste, coconut milk, a pinch of sugar, and additional salt. Stir well and bring to a boil. Reduce the heat and let it simmer uncovered for 10-15 minutes, stirring occasionally.
Carefully transfer the sauce to a blender and blend until smooth. Return the sauce to the pan.
Add the marinated prawns to the sauce, ensuring they are submerged. Simmer over low heat for 3-5 minutes until the prawns are pink and cooked through.
Taste and adjust the seasoning as needed. Remove the cardamom pods before serving.
Serve the curry with basmati rice, garnished with fresh coriander leaves.