Preheat oven to 350 deg F
Cut squash in half and deseed. Place halves on a baking sheet, cut side down. Bake until tender when pierced with a knife, 45 mins to 1 hour. Scoop out flesh when cool enough to handle.
Heat oil in a saucepan over medium heat. Add celery, onion and carrot and stir to coat. Cover, reduce heat to medium-low and cook, stirring frequently, until soft, 8-10 mins. Stir in the squash flesh, cumin, chipotle to taste and cloves. Add broth and simmer, covered, until the vegetables are tender, 20 to 25 mins.
Puree the soup until smooth. Season with salt and pepper. Garnish with drizled yogurt and sprinkle of chives (or parsley)