Preheat the oven to 200°C/180°F/Gas mark 6
Mix together the mirin, soy sauce, sugar, sesame oil, rice wine vinegar, garlic and ginger in a small bowl. Divide the mixture in half and add the miso paste to one half, setting the other half aside.
Lay each piece of cod on a piece of greaseproof paper large enough to enclose it, spoon the miso mix onto the fish and scatter over the coriander. Tightly seal to make parcels.
Put the 4 parcels into a baking dish, transfer to the oven and bake for 8-10 minutes.
In a bowl, add the beans, peas, spring onions and radishes to the leftover dressing and toss until evenly coated.
Divide the salad between 4 plates.
Unwrap the parcels, lift out the cod and serve on top of the salad, with extra coriander leaves and lime wedges on the side.