Since we don't have the source code for the widget, I don't think we can do this. The workaround would be creating a custom widget that functions similarly and fetches recent content.
Also, you mentioned 'theme files', are you using Jive 7?
If you're on a hosted instance, it looks like this table comes from jive-macros.ftl. Be careful though as these are shared macros, so modifying them may affect other widgets, not just Recent Content.
Thank you very much Scott. Let me looking into it.