Open the cans and pour off the juice. Put the corn and tuna in a large enough bowl. Cut the spring onions into small thin rings and add them to the bowl.
Fold in 3 - 4 tablespoons (can be more) of the mayonnaise and mix well. Season to taste with salt and pepper. Put in the fridge and let it steep for about half an hour. Super delicious as a side salad or on toast.