This paper describes a research through design project for reducing student’s food waste in a Swedish high school canteen. It was found that the design outcome is influenced by how a designer approaches the chosen problem space of sustainability. Building only on the existing perspectives of eco-feedback technologies and persuasive frameworks within interaction design, immensely constrains the role interaction design could take in working with sustainability issues. The complexities of sustainability related problems should be seen as a rich opportunity space to approach by design. Ethnographic research methods should be used when designing for sustainability. Found strengths of interaction design within design for sustainability were the data measurement of consumption and change. Together with the communication possibilities of digital and connected devices. The design outcome became a digital tool for kitchen staff to use when evaluating the lunch menu. The research also led to four suggestions for future design projects.