Cut the fish fillets into portions, season with salt and rub in a little lemon juice. Let it steep in the refrigerator for at least half an hour.
Finely dice the onion and fry in the oil in a large pan until golden. Grate the garlic cloves and ginger in a mortar to a paste or chop very finely and roast with the onions for a minute. Add turmeric, coriander powder, cumin and chili powder and let it steep for a moment. Next, add the coconut milk, the green chili peppers cut into thin strips, the remaining lemon juice and the vinegar. Let it boil down on a low flame for almost ten minutes. Season to taste with salt.
Put the fish pieces in the sauce and let simmer covered for five to six minutes. Finely chop the fresh coriander and mix in.