Heat 1 1/2 teaspoons oil in a Dutch oven over medium-high heat. Add onion and minced garlic; sauté 5 minutes or until tender. Add zucchini, broth, 1/2 teaspoon salt, and 1/2 teaspoon pepper; bring to a boil. Reduce heat, and simmer 25 minutes or until zucchini is very tender. Let stand 5 minutes.
Place half of the zucchini mixture in a blender; cover tightly, and process until smooth. Pour pureed zucchini mixture into a large bowl. Repeat procedure with remaining zucchini mixture. Place pureed zucchini mixture in pan. Cook over low heat 5 minutes or until thoroughly heated. Keep warm.
Preheat oven to 400°.
Place bread slices in a single layer on a baking sheet. Coat bread with cooking spray. Bake at 400° for 5 minutes or until toasted. Rub bread with cut sides of garlic clove.
Place parsley, tarragon, and chives in a small bowl. Combine 1 1/2 teaspoons oil, juice, 1/8 teaspoon salt, and 1/8 teaspoon pepper. Pour over parsley mixture; toss well.
Spoon 1 cup soup into each of 8 bowls. Divide parsley mixture evenly over toasted bread slices. Top each serving with 2 bread slices. Serve immediately.