Begin by pre-heating your oven to 200C / 392F / gas mark 6 and line a loaf tin with grease proof paper and place to one side.
Peel the butternut squash and cut 6 thin circles from the neck of the squash.
Lay the butternut squash circles in the bottom of the loaf tin, overlapping slightly.
Next, roughly chop the celery, remaining butternut squash and onion.
Add this to the food processor/blender and pulse until you've achieved a roughly diced texture..
Place the chopped celery, butternut squash and onion into a pan with 1 tablespoon olive oil and a big pinch of salt and cook on a medium heat for 5 minutes or until soft.
Next dice the mushrooms (again using the pulse setting of your food processor/blender) and add to the pan along with the minced garlic and cook for 5 minutes, stirring regularly.
Add the lentils to the pan and simmer on a low heat until all of the liquid from the mushrooms has evaporated.
Set the pan to one side and allow to cool completely.
Next, place the white bread into the food processor / blender. Turn it on a low, constant speed and blend until breadcrumbs have formed. Place the breadcrumbs into a bowl.
Add the chestnuts, walnuts and herbs to the food processor / blender and pulse until you've achieved a coarse, chopped texture.
Add these to the breadcrumbs.
Stir the breadcrumb mix into the vegetables in the sauce pan until fully combined. Add the melted butter to bind and season to taste.
Spread the nut roast mixture over the butternut squash circles and smooth out until it is level.
Cover the tin with foil and bake in the centre of the oven for 30 minutes.
Once the 30 minutes is up, remove the foil from the nut roast and heat uncovered for 15 minutes or until the loaf feels firm to the touch.
Remove the nut roast from the pan by flipping it out onto a serving dish and removing the grease proof paper.