Paper from my already published PhD thesis -- How do I cite it?
Yes, you can publish a chapter of your thesis as a journal paper. The two-year time lag is slightly unusual, but it's not a show-stopper. However, since the thesis has been cited already, it is possible that someone else may publish a work that extends the results of the chapter you intend to publish, which might lead to rejection. You should be prepared for that. 

I would also cite the thesis, in the introduction or perhaps in an acknowledgment section (depending on the intended journal; have a look through the archives to see common practices). "Some/The majority/Most of the materials contained in this paper were previously published (in modified form) in my thesis ...".