If you had your interviews already then good luck with the result!
For the subject I would say you could talk about anything you are passionate about and that you think a) is appropriate for the setting and b) you think the interviewers will find interesting. I think you are not encouraged to talk about things that have been covered in your application. You should show that a) your English fluency is of a good level, and b) you are an interesting person with interesting things to say. If you covered these you should be fine.
gwendole
Rohitrai,
I see that you are matriculating to HEC in September, congratulations! I have my interviews next week. I had decided to do a presentation on issues in international restructuring (my background), but I just found a chat with admissions on line that discouraged doing a professional presentation. What topic did you choose?