Due to its purchasing power, the public food service sector is viewed as a potential transformative driver towards sustainable food systems. Organic meal planning and regional procurement may be a vital implementation strategy towards Planetary Health Diets in the communal catering arena. Capable of unleashing desirable synergies within local foodsheds, this transition pathway can potentially benefit all stages of the value chain, while also positively influencing consumer dietary behavior. Transformation, however, poses complex challenges to caterers, as it demands a shift in mindset regarding the philosophy, organization, and management of cafeteria systems as well as the need for affordable and aggregated supplies of source-identified local organic foods. This action research case study engaged the public caterer of a German University, undergraduate students, and additional stakeholders in a Living Lab to develop a weekly farm-to-table cafeteria menu, including its actual preparation, based on a conceptual sustainability standard. Hence, through an iterative process, involving two feedback cycles, an ambitious set of nutritional and procurement criteria were devised, inspired by the external input from exemplary practitioners in the field of green cuisine and procurement. The resulting meal plan was then subjected to an evaluation vis-á-vis its compliance with (1) dietary recommendations, (2) seasonality, (3) organic certification, (4) a defined foodshed boundary, (5) budget neutrality, and (6) life cycle assessment.