Meanwhile, heat the oil in a large pan, then fry the onion over a medium-high heat for 5-6 mins, stirring occasionally, until golden and softened. Stir in the garlic and cook for a further 2-3 mins. Drain the peppers, reserving their juice, then stir into the onion. Cook for 2-3 mins to heat through. Blitz the mixture in a food processor, with 75ml/2½fl oz reserved juice from the peppers and 75ml/2½fl oz cooking liquid from the pasta, to make a chunky sauce.
Drain the pasta and return it to the pan. Add the pepper mixture, then season to taste. Toss with the rocket or watercress while still hot, so it just begins to wilt, then serve.
Recipe from Good Food Vegetarian Christmas magazine, December 2006