Combine the bacon and 1/4 cup water in a large nonstick saucepan over moderate heat. Cook, stirring occasionally, for 5 minutes or until the bacon has rendered its fat. Add the onion and cook for 7 minutes or until golden brown and tender.
Add the rice, stirring to coat. Add the stock, 1 1/2 cups water, the pepper and a pinch of salt, and bring to the boil. Reduce to a simmer, cover and cook for 15 minutes. Stir in the peas and parsley, cover and cook, stirring occasionally, for 10 minutes or until the rice is tender and the peas are heated through. Stir in the Parmesan and butter.