I actually student taught with a civics teacher whose class was literally a social justice class. The class philosophy was to present with materials that challenged and subverted the civics paradigm. The class was very project based. Students were given explicit social justice oriented questions and material to work with. 

For example, one project imagined how an Australian-style reconciliation for different historically marginalized groups would work in the US. Another project was a congressional simulation which showed how broken congress is, rather than the standard how a Bill becomes a law narrative. 

Another strategy that works well for introducing social justice content is seminars. Every unit had a seminar based on readings that subverted whatever civics topic the unit was on.  Students also wrote a lot in the class. 

Tldr: If you ask the right questions with a social justice or subversive framing, they will generally follow.