HEAT THE OIL IN A STOCK POT over low heat, add the onions and slowly cook, stirring, for about 7 minutes. Do not let them color. Add the carrots and continue cooking, stirring, until most of their water has been released and they fall apart, about 35 minutes. Add the stock, cover, bring to a boil, reduce the heat and simmer about 15 minutes. Add the cantaloupe, salt, coriander and cumin and cook 2 minutes. Strain and reserve the liquid. Transfer the carrots, onions and cantaloupe to a blender or food processor and puree until very smooth. Return the puree to the pot and add the reserved liquid. Chill in refrigerator for 2-to-3 hours. Combine the milk and the yogurt in a small bowl until smooth. Reserve until serving. Pour the soup into chilled soup bowls just before serving. Decorate the surface by spooning 3 simple lines of yogurt mixture across the surface of each bowl of soup. Using the handle end of the spoon, lightly drag across the 3 stripes at a 90-degree angle to make a "feathered" decoration.