Is there is gel treatment for mucositis?

Yes. A variety of treatments are available for mucositis. See - http://oralcancerfoundation.Org/treatment/mucositis.Html. Commercially available or "compounded" gel therapies may be available to help treat mucositis. Gels may act as a barrier protection while other therapies may work in other ways.
SEE O.S. Dr. Mucositis is a very general term. The question should be : "mucositis caused by?" try to see an oral surgeon if it is in your mouth.