Heat the oven to 200C/180C fan/gas 6. Put a pan of water on a high heat. When it boils add the potatoes, then turn the heat down and simmer for 10-12 mins until tender.
Meanwhile combine all of the salad ingredients, reserving a little coriander. Season lightly. Once the potatoes are cooked, drain and run under cold water to cool. Drain again and toss through the salad.
Rub the oil over the cod fillets, then put on a non-stick baking tray and lay a few ginger and lime slices on top of each fillet. Put in the oven and cook for 6-9 mins, depending on thickness.
Divide the salad between four plates, then top with the cod and remaining coriander.