As you have chosen to be anonymous, it is not possible to find out your background. Since you are teaching MBAs, I am sure that you have a Master's degree. Did you study Research Methodology as a subject? If so, you should know how to go about selecting a topic.
I found some ideas for topics at
https://dissertationsage.co.uk/disse...ce-management/
Kindly drop me a Private Message giving more details about your qualifications, where you would like to do your PhD, and in what mode, etc.