Peel and finely chop onion and garlic and fry in olive oil until translucent. Peel the tomatoes, cut them into small pieces and add to the braised onion with the vinegar. Season with salt, pepper and sugar and pour in the vegetable stock. Let the sauce stew for about 20 minutes.
Cook the pasta in salted water until al dente.
Drain the tuna and roughly chop it, pluck the dill and chop (put some stalks aside for decoration).
At the end of the cooking time, heat the tuna, dill and capers in the sauce.
Either mix the pasta into the sauce or serve it separately. Garnish with creme fraiche and dill if you like.