The rapid deployment of 5G and beyond necessitates efficient and scalable cell site provisioning. Open Radio Access Network (OpenRAN) architectures, while promoting vendor diversity and flexibility, introduce complexities in the deployment process. This paper presents a novel approach to automating cell site deployments for multi-vendor OpenRAN environments, addressing a key challenge identified in existing research. We propose a structured framework utilizing macro-milestones (MaM), each with defined pre-checks, actions, and post-checks, to ensure a robust and reliable deployment process. A key aspect of our approach is the use of Zero-Touch Provisioning (ZTP) as a trigger for the automation pipeline, minimizing manual intervention. We demonstrate the efficacy of our solution through a lab setup mirroring real-world telecom networks using a combination of commercial-grade and open-source components. The execution results showcase the solution's ability to provision cell sites efficiently within a commercially acceptable timeframe, achieving an overall success rate of 90%. The paper provides a detailed analysis of individual milestone provisioning times, common error types, and their impact, offering valuable insights for practical deployments. This research significantly contributes to the field of cell site automation by presenting a practical and effective solution for deploying complex, multi-vendor OpenRAN architectures, essential for meeting the demands of next-generation wireless networks.