1. Remove roots, outer leaves, and tops from leeks, leaving white and light green parts of each leek. Cut each leek in half lengthwise. Cut each half crosswise into thin slices. Rinse with cold water; drain.
2. Heat olive oil in a large Dutch oven over medium heat. Add leeks to pan; cook 10 minutes or until tender, stirring frequently. Add cumin and garlic; cook for 1 minute.
3. Add chicken broth and chickpeas; bring to a boil. Reduce heat to medium-low, and simmer 15 minutes. Stir in parsley. Place about 2/3 cup bread in each of 6 bowls; ladle about 1 1/3 cups soup over each serving. Combine 3/4 cup plain low-fat yogurt and 6 teaspoons harissa in a small bowl. Top each serving with 2 tablespoons yogurt mixture.