Serious concerns have been raised about social media's and online news outlets' contribution to a pandemic of misinformation. The sheer volume and tendency of misinformation to exploit people's cognitive biases have eroded the public's trust in media outlets, governmental institutions, and the democratic process. With Human-Computer Interaction being at the forefront of designing and developing user-facing computing systems, we bear special opportunities to address these issues and work on solutions to mitigate problems arising from misinformation. This workshop brings together designers, developers, and thinkers across disciplines to redefine computing systems by focusing on technologies and applications that instil and nurture critical thinking in their users. By focusing on the problem of misinformation and users' cognitive security, this workshop will sketch out blueprints for systems and interfaces that contribute to advancing technology and media literacy, building critical thinking skills, and helping users telling fake from truth.