First, slice the butternut squash in half and scoop out the seeds and discard.
Using a spoon, hollow out most of the squash.
Wash and chop the spinach, place in a pot with a pinch of salt and sweat until the spinach is cooked approximately 5 mins, season with a little fresh nutmeg.
In a pan, with a little olive oil, fry the onion, celery, mushrooms, add the butter, rosemary, chilli, nutmeg, and flesh of the squash.
Cook slowly for 5 minutes. Remove from the heat and allow to cool, Season.
Stir in the egg, orange zest, chestnuts, cheddar and mix in enough breadcrumbs so that the stuffing is not too sticky.
Fill both halves of the squash with the stuffing, stick them back together and wrap the whole squash in a double layer of tin foil.
With a rolling pin or your fingers, make a one inch indent down your stuffing on each half, divide the cooked spinach between the two halfs and place in the indentation. Bake the squash in the oven for 1 ½ hours.
To check its ready push a small knife into it and it should come out easy.
Unwrap and place on a serving plate a bring to the table.