Preheat the oven to 450°F and spray a large rimmed baking sheet with nonstick cooking spray. Cut the pumpkin in half and scoop out the seeds. Reserve the seeds. Cover the pumpkin with aluminum foil and roast for 40 to 45 minutes, until very tender. Remove from the oven and let cool slightly.
Toss the onion, apple, and garlic with the olive oil on a large rimmed baking sheet. Season with salt and pepper. Roast for about 20 minutes, until the vegetables are softened and lightly caramelized.
When the pumpkin is cool enough to handle, scoop the flesh into the bowl of a food processor with the onion, apple, garlic, ginger, and warm chicken broth and blend until smooth. Season with salt and pepper, to taste.
Lower the oven temperature to 300°F and spray a large rimmed baking sheet with nonstick cooking spray.
Whisk the egg white in a medium bowl. Add the pumpkin seeds and stir to coat. Add the sugar, cumin, salt, cinnamon, and cayenne and toss to coat. Spread the pumpkin seeds out onto the prepared baking sheet. Bake for 30 to 35 minutes, turning every 10 minutes, until golden brown.
Ladle the soup into bowls and sprinkle the candied pepitas over the top.