Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Place the cubed butternut squash, chopped yellow onion, and garlic cloves on the sheet, then drizzle with olive oil and sprinkle with sea salt and black pepper.
Roast the vegetables for 25 to 30 minutes until the squash is fork-tender and slightly caramelized around the edges.
While the vegetables roast, season the chicken breast with a pinch of salt and sear in a pan over medium heat until the internal temperature reaches 165°F.
Transfer the roasted squash, onion, and garlic into a high-speed blender along with the chicken bone broth and ground nutmeg.
Blend on high until the soup is completely smooth and velvety, adding a splash more broth if you prefer a thinner consistency.
Slice the cooked chicken breast into thin strips or bite-sized pieces.
Pour the hot soup into a bowl, top with the sliced chicken and pumpkin seeds, and serve immediately.