Heat olive oil in a large saucepan over medium-low heat. Add onion and celery; cook 7 minutes or until onion is soft. Add the broth and next 6 ingredients (broth through bell peppers); bring to a boil. Cover, reduce heat, and simmer 40 minutes or until vegetables are tender.
Place half of the bell pepper mixture in a blender, and process until smooth. Pour pureed bell pepper mixture into a large bowl. Repeat procedure with remaining bell pepper mixture. Spoon soup into bowls; garnish with parsley, if desired