Add the sliced onion, mint leaves, and salt to a bowl. Mix well with hands and let it sit for 10 minutes.
After 10 minutes, you see water oozing out slightly. Squeeze the onions as much as you to get that water. Discard the squeezed water.
Now measure the onion, add either equal or little less yogurt, and mix well.
That's it. Onion raita is ready.
Video
Notes
I don't beat or whisk my yogurt separately. I directly mix it with the onion and mix well. You can beat it separately and with Greek yogurt; if you find it difficult to mix, add a tbsp of water but not more.
Adjust salt as required.
Please refer to the variation section for other add ons and ideas.