So I had a rant, and now I should recant.
I have now managed to get a favourite restaurant added on Onion Ring. I did this after they emailed their subscribers asking us to add restaurants. I couldn’t find the link to do so, so emailed them back with the details and they promised to make the link more visible.
The restaurant and review were added. Although the link to add a restaurant is still not as obvious as it might be (but then its generally quite a cluttered web site) but you will find an option to add an restaurant at the bottom of a results page.