Pre-heat the oven to 190°C/ Fan 170°C/ Gas Mark 5. Place the pumpkin halves on a baking tray and cook for 40 minutes.
Place the couscous in a bowl and pour over 100ml cold water and leave to stand for 10 minutes.
Heat 1 tbsp of the olive oil in a pan and cook the sliced leeks for 3-4 minutes before adding the mushrooms. Cook for a further 5-6 minutes, until the vegetables have softened.
Fluff up the couscous with a fork then stir into the leek and mushroom mixture with the pine nuts, parsley and crumbled feta cheese. Season with black pepper.
Spoon the stuffing mixture into the pumpkin halves, drizzle with the remaining olive oil and bake for a further 15 minutes.