Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Place the cubed butternut squash and the whole chicken breast on the baking sheet, then drizzle with olive oil.
Sprinkle the sea salt, black pepper, dried thyme, and dried sage evenly over the squash and chicken, tossing the squash to coat.
Roast in the oven for 25 to 30 minutes until the squash is fork-tender and the chicken reaches an internal temperature of 165°F.
While roasting, sauté the chopped onion and minced garlic in a small pot over medium heat until translucent and fragrant.
Remove the chicken from the oven and let it rest; add the roasted squash and vegetable broth to the pot with the onions.
Use an immersion blender to puree the squash mixture until it reaches a velvety, smooth consistency.
Slice the roasted chicken into thin strips and serve it directly on top of the warm soup bowl.