This paper examines Participatory Design (PD) as an epistemic practice that can strengthen how democratic institutions listen and respond to diverse forms of knowledge. Drawing on the PARliament Engagement project, it explores how creative approaches can reveal and reshape the interpretive practices that govern what counts as evidence in parliamentary scrutiny. The research was conducted through a participatory action research process involving ethnographic shadowing, interviews, and co-design workshops with parliamentary staff, creating opportunities for shared reflection on how knowledge is generated, interpreted, and used across scrutiny work. The paper develops the concept of institutional responsiveness to describe how PD can make interpretations of evidence visible, support organisational reflection, and build capacity for more inclusive and accountable decision-making. This positions PD not only as a method of engagement, but as a way of designing the infrastructures through which democratic institutions understand, evaluate, and respond to diverse forms of knowledge.