Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the cubed butternut squash with olive oil, sea salt, and black pepper, then roast for 25-30 minutes until tender and caramelized.
While the squash roasts, poach or pan-sear the chicken breast until fully cooked, then shred it into bite-sized pieces using two forks.
In a large pot over medium heat, sauté the chopped onion and minced garlic until translucent and fragrant.
Add the roasted squash and vegetable broth to the pot, bringing the mixture to a gentle simmer for 5 minutes.
Use an immersion blender to puree the soup until it reaches a smooth and velvety consistency.
Stir in the ground nutmeg and the shredded chicken, allowing it to heat through for 2 minutes.
Ladle the soup into a bowl and finish with a dollop of Greek yogurt before serving.