Original recipe: http://365daysofeasyrecipes.com/cucumber-radish-pickled-salad/
I made this recipe because - oddly enough for me - I had leftover cucumber and radishes, and wanted something kind of light to go with lasagna, so roasting the radishes wasn't really working for me.
I used a yellow onion for mine because that's what I had on hand, but the original recipe calls for a red onion, and that would give a really nice color contrast, but I don't think there is a huge difference in flavor between yellow and red. Maybe a little more punchy, so maybe use a small yellow onion instead of a medium red onion.
It doesn't appear that there is enough liquid for the veggies, so I went in after about an hour and tossed it again, and there was more liquid. So I part of the minimum 2 hour time to sit is to let all the moisture come out and coat everything well. But it tastes amazing - Steve really liked it!