Heat oil in a large saucepan over medium heat. Add celery, minced onion, bell pepper, and carrot. Cook 10 minutes or until tender, stirring occasionally. Add garlic and the next 4 ingredients (through black pepper); sauté 3 minutes. Add broth, water, and beans; bring to a boil. Reduce heat, and simmer 15 minutes. Cool slightly.
Place half of soup in a blender, and process until smooth. Pour into a bowl. Repeat procedure with remaining soup. Garnish with sliced green onions, if desired.