Purpose <p> This study aimed to assess the impact of peer-led cooking workshops on dietary knowledge, skills, and behavioral changes in adopting protein-rich cereals such as spelt, emmer, and einkorn among post-treatment cancer patients. It addressed barriers to sustainable dietary practices, contributing to improved well-being and alignment with the planetary health diet (PHD).</p> Methods <p>This cohort observational study, part of the BIOQUALIM protocol, adhered to STROBE guidelines and evaluated six post-cancer patients attending six bi-weekly, 2-h cooking workshops at Lyon Sud Hospital, France, between March and June 2024. Workshops focused on savory and sweet recipes using protein-rich cereals (spelt, einkorn, and emmer). Data were collected and analyzed following Kirkpatrick’s four-level model using pre- and post-workshop questionnaires (Wilcoxon test analysis) and semi-structured interviews (thematic analysis).</p> Results <p>Participants demonstrated a significant increase in knowledge of protein-rich cereals (mean score improvement from 1.9 to 4.0, <i>p</i> = 0.035) and a non-significant improvement in their skills (from 2.5 to 4.1, <i>p</i> = 0.063). Participants reported improved digestion, well-being, and increased confidence in adopting such plant-based diets. The thematic analysis showed that group dynamics fostered social support and self-efficacy. Obstacles such as ingredient availability and preparation time were identified.</p> Conclusion <p>Peer-led cooking workshops effectively promote dietary knowledge, sustainable practices, and well-being in post-cancer patients, aligning with PHD principles. This intervention demonstrates potential as a scalable approach for integrating sustainable and health-promoting dietary behaviors. Further research with larger, diverse samples is needed to enhance generalizability and long-term impact assessment.</p>