Preheat your oven to 400°F. Peel, seed, and cube the butternut squash into even pieces.
Toss the butternut squash with olive oil, salt, and pepper, then spread it on a baking sheet lined with parchment paper.
Roast the squash in the oven for 25-30 minutes or until tender and slightly caramelized, stirring halfway through.
While the squash roasts, finely chop the yellow onion and mince the garlic.
In a large pot, heat a small drizzle of olive oil over medium heat. Sauté the onion until translucent, then add the garlic and cook for an additional minute.
Add the roasted squash, vegetable broth, and cannellini beans to the pot. Bring the mixture to a simmer for about 5 minutes to meld the flavors.
Remove the pot from heat and use an immersion blender to blend the soup until smooth and creamy. For an extra silky texture, you can blend in batches using a countertop blender.
Return the soup to low heat and stir in the nonfat Greek yogurt gradually, ensuring the soup is warm but not boiling to prevent curdling.
Season with nutmeg, additional salt, and pepper as needed. Serve immediately and enjoy your healthy, protein-packed creamy roasted butternut squash soup.