Preheat the oven to 400°F.
In a shallow baking pan, toss the squash with the oil and salt. Roast 20 minutes or until tender.
In a soup pot, combine the squash, onions, and chicken stock. Simmer until onions are very tender, about 20 minutes. Puree the soup with an immersion blender until smooth. If too thick, add additional chicken stock. Adjust the seasonings and add the cream. Serve hot in soup bowls. Top each serving with a cheese slice and pumpkin seeds. Serve immediately.