Preheat the oven to 160°C/325°F/gas mark 3.
Cut the squash in half lengthwise and scoop out the seeds and stringy fibre in the centre. Pour the water into a large roasting pan. Cover each cut-side of the squash with a tablespoon of olive oil and a sprinkling of sea salt and pepper. Turn the squash halves face-down in the roasting pan. Roast, uncovered, for approimately 1 hour until the skin of the squash is easily pierced and the “meat” is soft.
Remove from the oven and set aside to cool. In a soup-pot set on medium heat, pour 3 tablespoons olive oil. Add chopped onion and apple, sautéing for about 10 minutes until soft and onion is translucent. Add chopped garlic. Sauté for a few more minutes. Add vegetable stock and allow to come to boil. Add a pinch more salt and pepper, and the ground coriander and nutmeg. Reduce to a simmer and cover.
Scoop out cooled squash and add to the soup mixture. Bring soup up to a boil again, then reduce again to a simmer. Leave to simmer for another 10 minutes. Turn off heat and let cool to room temperature.
Pour soup mixture into blender and puree. Pour back into soup-pot. Heat before serving. For a garnish, try a small dollop of yoghurt, if dairy is ok for you and your guests.