I am rather new to chicken raising, so I don't know a whole lot of options as to what it could be, but from your picture, it looks exactly like my chicken's problem. If she does have the "fungal junk", I am going to say it's canker. You can look at my link/post and see what the images looked like I opened my chicken's mouth and it had that yellow cottage cheese looking growth. Since I have been giving her that medicine listed above, it has greatly improved and she only had a tiny little lump now, after about a week. Your chicken's lump is bigger than what my chicken's was. But you should go ahead and take care of it before it spreads further. Canker is known to be fatal if in certain places, and can be contracted from chicken to chicken.