Preparation Cook onion, carrots, celery, garlic, and bay leaf with 1/2 teaspoon salt in oil in a wide 5- to 6-quart heavy pot over moderately high heat, stirring occasionally, until vegetables are softened, about 5 minutes. Stir in tomato paste and cook, stirring, 1 minute. Add broth, water, chickpeas, 1/4 teaspoon pepper, and remaining 1/2 teaspoon salt and simmer briskly, covered, until vegetables are tender, about 15 minutes. Discard bay leaf. Transfer 1 cup soup to a blender and purée, then stir back into soup. Stir in arugula and remaining 1/4 teaspoon pepper and cook just until arugula is wilted, about 1 minute.