Preheat the oven to 425 F.
Peel and seed the squash, and then cut the squash, onions, and apples into1 inch chunks. Place them in a single layer on two baking sheets, and mix with the olive oil. Season the mixture with 1 teaspoon salt and 1/2 teaspoon pepper, and roast for approximately 45 minutes. Turn once during roasting so everything is evenly cooked.
Add the chicken stock and roasted vegetables to a soup pot. Puree them with an immersion blender, add 1 teaspoon salt, 1/2 teaspoon pepper, and the curry powder (I use hot madras-style, but we like things fairly spicy). Heat to a simmer, taste, and adjust seasonings as necessary. Additional stock can be added if the soup is too thick. Serve with scallions on the side for garnish.