Boil 1 cup spinach leaves in water with ½ tsp of salt for 3 to 4 minutes and then transfer them immediately to a bowl with ice cubes. Dip them and remove them on a plate.
Blend 1 cup fresh pieces of coconut, 10 garlic cloves (peeled, whole), a piece of ginger (1 inch in size, roughly diced), 6 pieces of whole green chilies, 15 pieces of curry leaves, 1 tbsp of coriander seeds, 20 pieces of black peppercorns, 5 pieces of cloves, pre-blanched spinach leaves, 1 cup of coriander leaves with ½ cup of water in a blender.
Then add 1 tbsp of tamarind (soaked in water) and 1 tbsp of salt and blend again. Check the final consistency. Transfer it to a bowl.
Put in 500 grams of Surmai fish (or any other variety with less bones), coat them nicely with the green masala, cover the bowl and keep it aside for an hour to marinate properly.
Put the marinated fish pieces only in 1 tbsp cooking oil. Flip, cover and fry both sides for a couple of minutes each on a medium to high flame till they are slightly charred. Check and remove the pan.
Fry 5 pieces of crushed garlic cloves in 1 tbsp of cooking oil until brown and then add 10 pieces of finely chopped curry leaves. Add the green masala paste, stir, cover and cook over a low to medium flame for about 5 minutes. Then, add 1.5 cups of water. Cover and again cook over a low to medium flame for about 5 minutes and bring it to a boil. Check the consistency and salt. Add if needed.
Add the fish pieces, cover and cook for 10 minutes more, check the doneness, and finally garnish with a few chopped coriander leaves.
Your tasty and spicy green masala fish curry is ready. Serve it with rice or roti.