Heat the oil in a large saucepan over medium heat. Add the onion, garlic, carrots and celery and cook, stirring, until softened, 5-7 minutes.
Add the squash, yam, spices, stock, coconut milk, salt and pepper, and bring to a simmer. Cover and simmer for 20 minutes or until the vegetables are very tender.
Purée with an immersion blender or regular blender. Stir in the vinegar and adjust the seasoning.
Combine the cumin yogurt ingredients in a bowl. Purée in a blender if you like a very smooth consistency.
To serve, divide the bisque between bowls, top with cumin yogurt and garnish with pumpkin seeds, fried shallots and cilantro.