Enhancing and maintaining food supply chain efficiency is a critical challenge. Due to its complexity and multi-agent nature, achieving a comprehensive understanding of the entire system is difficult, and even with a holistic view, no single entity can exert full control. Therefore, an effective mechanism is needed to facilitate cooperation among supply chain entities to improve overall performance. As a first step toward this goal, this paper focuses on lettuce supply chains in the United States and Japan and models them as a system of interconnected subsystems using a system-of-systems architecting approach. Based on a literature review, site visits, and interviews, this paper identifies key subsystems and their interfaces and analyzes differences between the two supply chains.