The most operationally efficient solution for turning on AWS CloudTrail across multiple AWS accounts managed within an AWS Organization is to create a single CloudTrail trail in the organization's management account and configure it to log events for all accounts within the organization. This approach leverages CloudTrail's ability to consolidate logs from all accounts in an organization, thereby simplifying management, reducing overhead, and ensuring consistent logging across accounts. This method eliminates the need for manual intervention in each account, making it an operationally efficient choice for organizations planning to scale their AWS usage.

AWS CloudTrail Documentation: Provides detailed instructions on setting up CloudTrail, including how to configure it for an organization.

AWS Organizations Documentation: Offers insights into best practices for managing multiple AWS accounts and how services like CloudTrail integrate with AWS Organizations.

AWS Best Practices for Security and Governance: Guides on how to effectively use AWS services to maintain a secure and well-governed AWS environment, with a focus on centralized logging and monitoring.