Heat oil in a large Dutch oven over medium heat. Add onions; sauté 3 minutes. Add carrot and potato; cook for 1 minute. Add ginger and remaining ingredients; bring to a boil. Cover. Reduce heat; simmer 1 hour. Discard bay leaves. Place 6 cups in a food processor; process until smooth. Return to pan, and stir well. Garnish with green onions, if desired.