Tunafish and Spring Onion Sandwich

Tinned tuna is a really versatile store-cupboard item. Don’t automatically sneer at tinned or even frozen products. Hawaiian yellowfin tuna may be one of the world’s great fish to eat fresh, but I have no easy access to it. Nor would it suit my sandwich as well as tinned supermarket bonito. More important to worry about is the bread. Flabby white sliced will not do.