Heat the oil in a large heavy-bottomed saucepan over a medium–high heat and fry the pancetta until crisp. Reduce the heat to medium, add the onions and cook for about 10 minutes, until soft. Add the chilli and rosemary and cook for 2 minutes.
Chuck in the wine and increase the heat to burn off the alcohol; stir to deglaze the pan. Add the tomatoes and check the seasoning.