Place the stock in a medium nonstick pan, bring back to the boil and add the pasta.
Meanwhile, melt the butter in a small frying pan and add the garlic and pancetta. Fry for 2 minutes until the pancetta is crispy.
Add the pancetta and garlic to the orzo with the peas and continue to cook over a moderate heat for about 7 minutes until al dente, stirring from time to time to prevent the pasta sticking and adding a little more water if necessary.
Season to taste and stir in the parsley and most of the Parmesan, reserving a little for garnish. Serve immediately, sprinkled with the reserved Parmesan and freshly ground black pepper.