In a small food processor or blender, puree all paste ingredients, adding water a few tablespoons at a time until smooth.

Place a large shallow pan over medium heat. Add the oil and cook until it shimmers, then add the curry leaves, if using, and saute for about 1 minute until fragrant. Add the onion and saute for 3-4 minutes until translucent, then add the tomato and reduce the heat to medium. Continue cooking, stirring occasionally, until the tomato pieces begin to break down, then add the ginger and jalapeno if you like your curry spicy. Continue to cook for another two minutes until the scent of the ginger mellows.

Pour the paste into the pan. Add a cup of water to the food processor/blender bowl to rinse out, then pour into the pan as well. Stir well and bring to a simmer for five minutes, then stir in the tamarind paste.

Lay the fish into the pan and spoon a bit of the curry sauce over each piece. Cover the pan and reduce heat to low, cook fish for 5-7 minutes until its opaque. Remove the curry leaves.

Serve the fish and curry sauce over rice garnished generously with fresh cilantro.