Heat oil over medium high flame and saute garlic and onion until translucent (about 5 minutes). Add cucumbers and cook (stirring) for about 5 minutes more. Add stock and bring to a boil. Reduce heat and simmer about 12 minutes. Let cool to room temperature and puree in blender or food processer. Stir in yogurt and dill. Season with salt and pepper and keep chilled until ready to serve. Serve in chilled bowls.