Cook the pasta in 3-4 l boiling salted water (1 teaspoon salt per litre) according to the instructions on the packet. Drain the corn.
Peel onions and cut them into rings. Drain the tuna, heat the tuna oil in a pan. Brown the onions in it. Add tomatoes, corn, capers and 1 teaspoon of oregano, bring to the boil and simmer for 4-5 minutes.
Warm the tuna in the sauce, season with salt and pepper. Drain the pasta and mix with the sauce. Add Parmesan cheese.