Place a stock pot over a medium heat. Heat enough oil to coat the bottom of the pan, then throw in the mustard seeds.
Once the seeds start to crackle, add the fenugreek seeds, followed by the curry leaves, ginger and sliced onions. Cook until the onions are golden, stirring occasionally.
Add the turmeric powder, sauté briefly, then add the tomato puree and 200ml hot water. Add the chilli, cumin and coriander.
Cover the pan and bring to the boil for 20 minutes.
Turn down the heat, add the cubes of fish and allow to simmer for about 2 minutes. Stir the curry gently as it cooks, as the monkfish will cook quickly.
Add the coconut milk and season to taste before bringing the curry back to the boil.
Stir gently until the fish is cooked and the sauce full combined. Remove from the heat.
Serve with rice. Just before serving, sprinkle with the chopped coriander.