Flake the tuna into a bowl, then tip in the pine nuts, lemon zest, parsley, breadcrumbs, and egg. Season and mix together with your hands until completely combined. Roll the mix into 12 walnut-size balls. Put a large pan of salted water on to boil, then cook the spaghetti according to pack instructions.
Heat a little of the tuna oil in a large non-stick frying pan, then fry the tuna balls for 5 mins, turning every minute or so until completely golden. Drain on kitchen paper. Heat the tomato sauce, then toss together with the pasta and tuna balls.