1. First, make the pickled shallots. Top and tail the shallots, discard the peel and slice into thin rings. In a jar or small bowl, combine the vinegar and sugar and stir until the sugar has dissolved. Add the rings to the liquid, separating them into their individual layers. Ensure the shallots are completely covered and allow to pickle for at least 1 hour but ideally overnight.
2. Next, make your goujons. Take the fish and place on a clean chopping board. Cut into approximately 1cm x 6cm strips. In a shallow bowl, measure out the plain flour before seasoning well with salt and pepper. In a second bowl add your eggs before lightly whisking. In a third bowl, measure out the breadcrumbs.
3. Take the fish strips and first coat fully in the flour, knocking off any excess. Next, dip the strips into the egg allowing any excess egg to drip off, before finally adding to the breadcrumb bowl ensuring the fish is completely coated. Set the goujons aside whilst you heat the oil over a medium-high heat. Test the oil is hot using a small piece of bread - you want the oil to sizzle immediately when the bread is dropped in but not brown too quickly.
4. In batches, gently drop the goujons into the hot oil and allow to fry for 3 - 4 minutes until golden and crisp. Remove from the oil and place on some kitchen roll to drain off any excess oil.
5. Just before serving, make the salsa. Add the finely diced mango to a bowl along with the shallot, chilli and coriander. Squeeze in the juice of half a lime and cut the other half into wedges for serving. Stir all the ingredients together well.
6. When ready to serve place the fried goujons on a large serving board along with the bowl of salsa, soft tacos and shredded lettuce. In a small bowl simply combine the mayo and chilli sauce and serve to the table with the pickled shallots. Allow everyone to tuck in and build their own fish taco.