Put the fish steaks in a fairly shallow ovenproof dish with a lid, into which they fit quite closely.
Scatter the ginger, garlic, tomato, chilli and yellow pepper over and around the fish and the cardamom pods in between.
Empty the coconut milk into a separate bowl, add a good sprinkling of sea salt and gradually stir in the lime juice. Pour the mixture gently over and around the fish and cover the dish.
Preheat the oven to 150C/300F/Gas 2. Put the dish on the centre shelf and cook for 40-50 minutes, until the fish is lightly done. To discover this insert a small, sharp knife into the centre of one of the steaks - if the flesh is slightly darker pink in the centre it will be perfectly cooked. Remove from the oven.
Before serving scatter the mint leaves on top.