Preheat the oven to 220°C/gas mark 6. In a large frying pan over a high heat, cook the leek, bacon and thyme in the oil for 5 minutes, stirring constantly.
Add the barley and stock and bring to the boil. Transfer to an ovenproof dish and bake for 15 minutes. Stir in the frozen peas, cover and bake for a further 10-15 minutes until the barley is cooked and the stock absorbed. Season and serve sprinkled with the parmesan cheese.