This position paper examines the challenges and opportunities of participatory planning and design, with a focus on transdisciplinary action research and digital technologies. Drawing on insights from the TU Delft Citizen Voice Initiative and a workshop with academics, practitioners, and students, this position paper identifies key enablers of participation, including trust, transparency, reciprocity, and epistemic justice, while also addressing structural, institutional, and ethical barriers. Particular attention is given to power dynamics in participatory processes and the undervaluing of lived experience in relation to expert knowledge and bias. The paper further explores the role of digital participation, noting its potential to broaden inclusion through open-source platforms, gamification, and AI-based tools, but also highlighting risks related to accessibility, technological sovereignty, and the hype cycle of emerging innovations. Transdisciplinary action research is presented as a pathway to more collaborative and just practices, though it also faces institutional and ethical constraints. To advance participation in research, education and practice, the paper ends with 14 strategies that emphasise epistemic justice, inclusivity, long-term engagement, capacity-building, and experiential education that embed participation as a process rather than a one-off intervention.