Whizz the bread in a food processor to crumbs, tip into a bowl, then whizz half the sweetcorn until finely chopped. Add the chopped corn, remaining whole corn, tuna, cheese, spring onions and some seasoning into the bowl with the bread and mix well. Add the egg, bit by bit (you may not need it all), until the mixture is sticky enough to be shaped into four even-size burgers.
Heat the oil in a non-stick pan, then cook the burgers for 5 mins on each side until golden and hot through the middle. Stuff into wholemeal buns with your favourite lettuce and a good dollop of salsa.