Rub the inside of each half of the squash with extra virgin olive oil and sprinkle generously with salt and freshly cracked pepper. Place the squash halves cut-side down on a baking sheet lined with parchment. Place in an oven heated to 180°C or 350°F and bake for around an hour, depending on the size of the squash, until the skin pierces easily with a fork. Remove from the oven and scrape out the flesh with a spoon when cool enough to handle.
Add the squash to a soup pot and add vegetable stock until just covered, then cover and simmer. When the squash is very tender, blend the soup with an immersion blender, or in a stand blender in batches. Return to the pot and add the grated Gruyère cheese, and whisk in a small amount of butter, until creamy.
To serve, heat the bacon and chestnuts in a small pan over medium heat. Divide the mixture between bowls. Top with microgreens and toasted pumpkin seeds. Then drizzle in the soup on top to serve.