Heat the oven to 220C/fan 200C/gas 7. Roast the cod on a non-stick baking tray for about 10-12 minutes, depending on the thickness of the fillet, and once cooked remove from the oven. Discard the skin and any bones, and mash the fish in a bowl with a fork, as fine as possible, then allow to cool.
Mix all the remaining ingredients, except the oil, with the fish in a large mixing bowl, with a generous amount of salt and pepper, and then cover the bowl with clingfilm and chill the mixture for an hour to cool and solidify it.
Heat 1cm oil in a large frying pan over a medium-high heat and allow it to get hot, but not smoking. Take a heaped dessertspoonful of the mixture at a time and drop it into the oil. Don’t worry about uneven shapes. Fry the fritters for about 2-3 minutes, turning them over and frying them for about a minute on the reverse side, then remove using a slotted spoon and drain on to a kitchen paper-lined plate. Repeat until all the fritters are done.
Mix the sauce ingredients together with a little cold water, to slacken the mixture to a dipping-sauce consistency. Check the flavour and consistency and serve alongside the fritters, with lime wedges on the side.
