Chop the Perino tomatoes in half and place on a baking tray lined with parchment paper.
Top each tomato with a slice of garlic, a pinch of oregano, a sprinkle of salt and a dash of olive oil and place in the oven for 30 minutes.
Boil a large pot of salted water. Once the water is at a rolling boil, cook the pasta until al dente. Make sure to catch some of the cooking water for the sauce.
In a pan on medium heat, cook the finely diced onion with a little olive oil until translucent, add the tomatoes and smash together with the back of a wooden spoon.
Place the cooked pasta with a little of the water into the pot with the tomatoes and toss everything until well combined.
Serve in pasta bowls topped with shavings of parmesan and a few oregano leaves and season to taste.