Cook the pasta in 2 l boiling salted water (approx. 1 teaspoon salt per litre) according to package instructions.
In the meantime wash and halve the tomatoes. Peel and chop the onion. Peel garlic and chop finely. Clean, wash, dry and chop the arugula.
Heat the oil in a coated pan. Sauté the onion and garlic in it. Fry the cherry tomatoes briefly. Add the strained tomatoes, bring to the boil and simmer for 2-3 minutes. Season sauce with salt and chilli.
Drain the tuna. Add capers, heat briefly. Fold in the arugula. Drain the pasta and mix with the sauce.