Preheat the oven to 200°C/400°F/gas mark 6.
Carefully slice the tops off of the pumpkins and use a spoon to scoop out all of the seeds and stringy flesh.
Brush them inside and out with olive oil, make sure you do the tops too; then sprinkle with salt and pepper and arrange the pumpkins and their lids in a roasting tray.
Bake for around 30 minutes until the pumpkin flesh is tender. Remove from the oven and set aside.
While the pumpkins are roasting start preparing the rice. Heat the olive oil in a large pan and add the onion, celery, leek and carrot. Fry gently for about 10 minutes until soft and translucent.
Add the mushrooms, garlic and herbs and continue to cook until all of the excess water has evaporated.
Add the rice, stock, salt and a good grinding of black pepper. Bring up to a simmer then turn the heat down as low as it will go, cover the pan and cook for about 20 minutes until the rice is tender.
Remove from the heat and stir in the pecans and cranberries.
Divide the rice between the pumpkins, filling them right up to the top. Return to the oven for 10-15 minutes until heated through.
Serve the pumpkins topped with their lids.