Secondary research involves the summary, collation and/or synthesis of existing research. Secondary research is contrasted with primary research in that primary research involves the generation of data, whereas secondary research uses primary research sources as a source of data for analysis.
So a topic that is good to do secondary research on
As long as you are from Iran. I do suggest you conduct research on your context. For example "Teaching writing skills through English literature: Iran as an example". I did the same one, please check if it comes within your expectations from this question.
As Islam suggests, it would be a good idea to focus on your own EFL context.
One way of approaching this might be to think about your own experiences as an EFL learner/teacher.
What were the important problems that you /other learners/teachers encountered?
Secondary research could then focus on what existing primary research (particularly any from your own context) has to say about any one of these problems-
what , if anything, this suggests about the kinds of adjustments it would be good to make to teaching/learning /assessment approaches
which of these adjustments it might be possible to make in your context