To a large bowl, add the chopped squash, onion, apple and garlic. Season with salt, pepper and a pinch or two of chili or cayenne powder. Add the olive oil and toss to coat all ingredients well.
Spread the ingredients out on a baking sheet in a single layer. Roast for about 40 minutes, or until the squash is tender, shaking the pan to jostle the ingredients after 20 minutes.
Use a spoon to scoop the squash from the skin, discarding the skin. (Tip: Hold the squash pieces in a towel in one hand while scooping with the other. The towel will help protect hands from heat.) Place the peeled squash and remaining ingredients in a soup pot. Add the stock and bring to a boil over high. Cover and lower heat to a simmer; cook for 10 minutes.
Using an immersion blender, food processor or blender, carefully puree the ingredients until smooth, working in batches if necessary. If desired, add more stock to thin the soup to your liking.
Ladle the soup into 4 individual serving bowls. If desired, drizzle a little half & half over each serving. Top with pepitas and drizzle with additional olive oil. Serve warm.