Dip the chopped onion in olive oil, squeeze the garlic clove and add. Chop the tuna with a fork and fry with it.
Chop the tomatoes and add them to the pan. Let the whole thing simmer on a low flame for about 1/2 hour.
Put the pasta in boiling salted water and cook until al dente. Shortly before the end of the cooking time, season the tuna sauce with salt, pepper and chili peppers as desired.