Preheat your oven to 200°C/400°F/gas mark 6 and line a 900g loaf tin with baking parchment. If using the oil, heat it in a large frying pan. Alternatively, heat 2 tbsp of water or vegetable stock. Add the onion and mushrooms and cook over a medium heat until the onions have started to soften and the mushrooms have given out their liquid and it has evaporated off. They should be lightly golden in colour around the edges. If not using the oil, you may need to add more stock towards the beginning of the cooking process. Add the root vegetables and garlic and continue to cook, adding a little more stock if necessary, until they have collapsed down and reduced in volume. Stir in the herbs and remove from the heat. Put the lentils, nuts, chestnuts and breadcrumbs into a bowl and add the flax eggs. Season with plenty of salt and pepper and add the cooked vegetables. If using, put the prunes in a small saucepan, cover with the marsala and simmer until the liquid has all absorbed. Leave to cool. Cook the spinach, chard or kale in a little water until completely wilted down and squeeze out any excess liquid. Stir through the mixture along with the prunes, if using. Spoon the mixture into your prepared loaf tin and smooth over the top with a palette knife. Cover with more baking parchment to prevent the loaf from drying out. Bake in the preheated oven for around 1 hour until well browned and piping hot all the way through. Meanwhile, make the gravy. Heat the oil or 1 tbsp stock in a saucepan and add the shallot. Cook, adding more stock if necessary, until it has softened and caramelised. Add the mushrooms and continue to cook, adding more stock where necessary, until they DINNER have reduced in volume. Add the garlic and thyme and cook for a couple of minutes. Add the marsala or wine and bring to the boil. Allow to bubble up and reduce to almost nothing, then add the 400ml stock. Cover and simmer for around 10 minutes. If you want a thicker consistency, mix the cornflour or arrowroot with a little water and stir into the gravy. Continue to cook over a medium heat until the gravy thickens. Serve the nut and veggie roast with the gravy and a wide variety of vegetables.