Spread out the diced pumpkin onto a lightly greased baking tray. Roast in the oven for 30 minutes, turning once. Remove from the oven and reduce the heat to 180°C/350°F/Gas Mark 4.
Melt the butter in a saucepan. Add the red onion, celery and herbs and allow to cook over a medium heat for 5 minutes until soft, stirring frequently.
Crumble the stale bread into a large mixing bowl, add the onion mixture, egg, roasted pumpkin, stock and seasoning. Stir thoroughly to combine.
Transfer the stuffing to an oven-proof dish and cook in the oven for 40 minutes.
Slice into wedges and serve.
Notes
This make-ahead recipe can be stored in the freezer then defrosted and heated through in the oven.