How to mention your work in a peer-review?
If your paper is a relevant factor, then by all means mention it in peer review. I understand your concern about appropriateness, but in the situation you describe it seems unambiguous to me that you should recommend your own paper. 

If you are worried about it, there is typically a "confidential comments to editor" section where you could note that you're recommending your own paper but it's for a good reason. I wouldn't bother doing so unless, say, you've made four reviews in a row for the same journal and every one of them has the same recommendation.