In large saucepan, heat oil over medium heat; cook zucchini, onions, celery, garlic, curry powder, salt, cinnamon and pepper, stirring occasionally, for 10 minutes or until softened. Sprinkle with sugar; pour in stock and bring to boil. Reduce heat to medium; simmer for 20 minutes or until vegetables are very tender. In blender, pure zucchini mixture, in batches, until smooth. Pour into clean saucepan; reheat but do not boil. Season with more salt and pepper to taste. Try topping with a dollop of yogurt and a spoonful of chutney.