You have not provided sufficient information to answer your question. Did you have any documentation of the loan of the kiosk? Who signed the lease agreement with the shopping center? The answers to these questions can impact the answer to your question.
This response does not create an attorney-client relationship and is not intended to provide legal advice for your specific situation.
If you have a lease for it, have you gone to the landlord telling them another business is occupying your spot? Perhaps if they come by and tell him to get out he will. (They may not want to get involved, given that you let the other person in there, but you can try. They are supposed to give you quiet enjoyment of your space and just having some people from the mall come by and say "you need to go" might do the trick. Failing that, you might have to use an ejectment action in court. If so, you should hire counsel.
There is no substitute for the professional advice of an attorney who knows your case and represents you. My post is not, and may not be relied on as, legal advice and does not create an attorney-client relationship. Best wishes for a just and expeditious resolution.
Retain a lawyer and sue the borrower for replevin of your kiosk.
This is a summary based on incomplete facts. You should not rely on it as legal advise. No attorney-client relationship is intended to be formed. You may call me 772-562-4570; email me firstname.lastname@example.org, or visit my website http://www.millerlawoffices.us