Heat the pan to medium heat, add mustard seeds, cumin seeds, and curry leaves. Let them sizzle for a few seconds, then add chopped shallots and cook until soft and translucent.
Next, garlic paste and ginger paste and continue sautee until the onions are brown. Then add the chopped tomatoes and cook until the tomatoes are reduced and oil separates.
Add ground spices, turmeric, chilli, garam masala, and coriander powder. Stir it well for a few seconds until fragrant.
Pour the warm water in and let it simmer for 2-3 minutes. Then add the coconut milk and salt to taste. Bring it to a simmer.
Now, place the monkfish pieces in the curry sauce and cook for 3-4 minutes or until cooked through.
Stir in tamarind juice and green chillies. Let it cook for another 1-2 minutes. Turn off the heat and finish with coriander.
Transfer to a serving plate and serve with plain basmati rice, naan, or chapati.