writer choice topic related to TESOL research Phd.

I applied at a university for TESOL PhD and they respond that the research proposal I wrote was not strong enough for an offer. their comment were “Overall your proposal is a little under-theorised, the ga in teh literture not quite well enough justified, and the proposed topic not narrowed down enough. We recommend a more theoretical approach and narrowing down.” so I need a new proposal and I am running out of ideas. the proposal has to be clear, very detailed, interested”new” and at the same time not too complicated topic with no sources available. I well upload the proposal I wrote please follow the same formate and the same headings just with a new topic.