In a deep-sided frying pan, heat the oil over medium heat. Add the pancetta; cook for a few minutes before adding the onion. Once the onion have softened, add the peas and half of the beef stock; simmer over low heat for 5 minutes.
Add the remaining stock; cover and cook for 15 minutes. Check every 5 minutes or so to see if you need to add more liquid. Water or more stock will work fine. Season to taste with salt. Serve hot over pasta with freshly grated Parmesan cheese.