Finely chop the onion. Heat 2 tablespoons of olive oil and a knob of butter in a pan, add the onions and fry until lightly browned (about 7 minutes). Add the bacon and fry for a further 5 minutes, until it starts to crisp.
Add the rice and stock, and bring to the boil. Stir well, then reduce the heat and cook, covered, for 15-20 minutes until the rice is almost tender.
Stir in the peas, add a little salt and pepper and cook for a further 3 minutes, until the peas are cooked. Serve sprinkled with freshly grated parmesan and freshly ground black pepper.