Cook the spaghetti in plenty of boiling water according to pack
instructions. Meanwhile, finely chop the onion and tomatoes and
put in a large pan with the oil. Halve, deseed and finely chop
the chilli, then add to the pan. Gently heat through for a few
mins, stirring well.
Drain the pasta and add to the sauce, then break up the tuna
and add to the pan. Season if you like, then toss well and serve.