Peel the pumpkin, remove the seeds, and cut the flesh into equal cubes. Roughly chop the onion. Toast the pumpkin seeds briefly in a dry frying pan over medium-high heat until they begin to puff slightly, then immediately set them aside on a cold plate.
Heat a splash of oil in a large soup pot and sauté the chopped onion until translucent. Sprinkle the turmeric over it and cook for a minute to release its flavor. Add the pumpkin cubes and add just enough water so the vegetables are covered. Bring to a boil, lower the heat, and let simmer gently for about fifteen minutes until the pumpkin is completely tender.
Remove the pan from the heat and purée the contents with an immersion blender until smooth. Stir in the coconut milk to the puréed soup and mix everything together well until well combined. Place the pan back on low heat to warm the soup again, but make sure it does not boil.
Ladle the warm pumpkin soup into deep bowls or soup cups. Garnish the dish by sprinkling the toasted pumpkin seeds over it and serve immediately.