Bring the potatoes to a boil in plenty of salted water then lower the heat and simmer until tender. Drain well and leave to dry for a few minutes then return to the pan and mash until smooth. Set aside.
Flake the drained tuna into the mashed potato, mix in the spreing onions and parsley then season with salt, pepper and lemon juice. Divide the mixture into eight balls, then shape them into little cakes and dust lightly with flour.
Heat about 1 cm oil in a large frying pan and fry the cakes over a moderate heat for about 5 minutes per side, until they are crisp and brown. Drain on kitchen paper then serve with a green salad.