Cook the onions in 100ml of water until tender. Add the radishes and cook for about 2-3 minutes.
Add the honey and cumin seeds and cook for a further 5-6 minutes. The colour of the radishes will gradually start to run and form a glaze. When nearly all the liquid has evaporated, remove from the pan from the heat and season.
For the mackerel, preheat the oven to 180C/gas 4 or heat a barbecue until the coals are very hot.
Put two sheets of tin foil about the size of a broad sheet newspaper on the work surface (or you can use greaseproof paper if you are cooking in the oven).
Divide the shallots, lemon and herbs between the two pieces of foil. Sit the mackerel on top and score the skin with a sharp knife. Season with salt and pepper. Drizzle a tablespoon of water over the top and fold over the foil to form parcels.
Put the parcels on the barbecue or in the oven to cook for 8-10 minutes.
Open the parcels and divide the onion and radish mix between the two to serve.
Notes & Tips
Recipe reproduced with permission of Good Food Channel.