In a heavy-based saucepan, heat half the oil and slowly brown the pancetta or bacon for 5 minutes, then drain and set aside on paper towels. Add the onion and lightly brown for about 3 minutes, then add the chilli and cook for 2 minutes. Add the pancetta or bacon and the tomatoes, cover and cook over medium heat for about 20 minutes, then cook uncovered for a further 10-15