Preheat oven to 425 and line a rimmed baking sheet with foil.Toss the squash, carrots and onion with olive oil. Spread in a single layer on the baking sheet and season with salt and pepper. Roast until tender, about 30 minutes.Add the veggies to a blender along with the chicken broth. Puree until smooth (you can do this in batches if you need to.Pour the puree into a large saucepan. Add the chicken and spinach and simmer until the spinach is wilted. You can add more chicken broth to thin out the soup if you like.Season to taste with salt and pepper and serve!