How to deal with if you found someone is using your research proposal? I had submitted a research proposal to a group during Post Doc application in an university. But I did not join the same university for post doc. Now I got to know that they are conducting the same research I had proposed. 

How to deal with this? Though I am not working in the same area now, but it is my future plan. 

Is it really good to use other person's proposal?
Could that topic have been a relatively "generic" topic or a topic that is now fashionable? In which case it is not unlikely that people come up with similar ideas. Fashionable topics are unlikely to be exclusively yours. 

However, if it is an exotic idea, you may have been very unlucky. In which case, cut your losses and move on.