How to represent the Gantt chart on a Dashboard?

You will want to create a report of that project plan. I usually include the high-level details of the project plan and not all of the columns of information- base this on the audience that your dashboard is built for. Once you have created the report on your plan then you should be able to add it as a widget (report) to your dashboard, just ensure that your view within the report is set to Gantt.