For garnish: Add sour cream, 2 Tablespoons cilantro and 1 crushed garlic clove to a small bowl and stir until blended. Season to taste with salt and pepper. For soup: Heat oil in a large pan over medium heat. When hot, add onion and saute until softened. Add garlic an saute for 1 minute. Add zucchini and toss to blend. Add broth and bring to a boil. Cover and reduce heat to simmer for 10 minutes or until zucchini is very tender. Remove from heat, add 2 Tablespoons cilantro and let cool. Add soup to a blender and puree until smooth. Transfer back to pan, season to taste with salt and pepper and reheat. To serve, ladle soup into individual bowls and spoon a dollop of cilantro cream garnish in the center of each soup. Serve immediately.