Cut the pumpkin into large chunks and add to a stockpot. Rinse the lentils and add them to the pumpkin with the ginger and orange zest. Add the stock and over a medium heat bring the soup to the boil.
Reduce to simmer and cook until the lentils and pumpkin are both cooked (approx 30 minutes). Remove from the heat and transfer the ingredients to a food processor and process until smooth. Stir through the buttermilk top with chopped coriander and serve.
Note: Pumpkin is a great source of betacarotene and Vitamin A. On paper it has a high GI but because it's comprised of mainly water, and very little carbohydrate it can be enjoyed by everyone - even those concerned with high blood sugar levels.
Makes 4 servings (serve = 1 bowl)