Heat the oil in a frying pan then add the onion and cook for 4 minutes followed by the garlic for a further minute. Add the tomatoes, and season then allow to simmer for 25 minutes until thickened.
Cook the pasta according to pack instructions, adding the rocket to the water at the same time as the pasta.
Drain the pasta and rocket then add to the tomato mixture and toss together.
Garnish with the grated pecorino and serve immediately.