This study explores developing and implementing an online course to integrate Education for Sustainable Development (ESD) into the South African Curriculum Assessment Policy Statement (CAPS). The course design process emphasises the inclusion of Indigenous Knowledge Systems (IKS) and Sustainable Livelihoods as core components, fostering a transformative learning experience for teachers. Leveraging a Vygotskian action learning schema and expansive learning cycles, the course supports a co-engaged design research methodology to enhance teacher capacity in ESD. A 'theory of change' evaluation framework assesses the course's impact on curriculum strengthening. Key findings indicate that online teacher capacity-building programmes can effectively engage teachers, promote curriculum-activated ESD initiatives, and facilitate deeper integration of IKS and sustainable practices in school teaching. The hybrid design, combining online and face-to-face interactions, fosters a Professional Learning Community (PLC), which enhances teaching practices and learner engagement through realworld sustainability challenges.