The transition to more healthy and sustainable plant-based diets is urgently needed to tackle both health and environmental challenges. An important population growing up in the face of climate change is Generation-Z. These youngsters, today in their adolescence, may play a crucial role in the societal transition towards more sustainable plant-based diets. Although interventions focusing on both health and sustainability may be more powerful than those focusing on health alone, knowledge hereon is limited. Using mixed methods and co-creation, we will collect pioneering data on healthy and sustainable plant-based dietary patterns in adolescents (14–18 years), including those with lower socio-economic backgrounds. We will investigate how they can be motivated to shift towards more healthy and sustainable plant-based diets by increasing our understanding of the capabilities, opportunities, knowledge, perceptions, facilitators and barriers to eat healthy and sustainable plant-based foods. Also, intervention settings for the promotion of healthy and sustainable plant-based diets will be determined, together with the target group. Finally, we will develop and pilot-test a co-created intervention. This project will enrich the knowledge base and deliver a ready-to-use intervention aimed at shifting Generation-Z towards more healthy and sustainable plant-based diets, taking different socio-economic backgrounds into account.