Preheat the oven to 375°. Butter a medium baking dish. Season the squash with salt and set it cut side down in the baking dish. Bake for about 1 hour and 10 minutes, until the squash is very tender. Let cool slightly.
Meanwhile, spread the pecans in a pie plate and toast for about 7 minutes, or until fragrant. Let cool, then coarsely chop and transfer to a medium bowl. Add the banana and maple syrup and stir to coat.
Peel the squash. In a blender, puree the squash, water, crčme fraîche and cinna- mon until very smooth. Transfer to a medium saucepan and warm over low heat. Ladle the soup into bowls, garnish with the banana-nut topping and watercress and serve hot or at room temperature.