After a tsunami, any plate left out in the sun will be sure to get warm. The tsunami knocked this plate out of the kitchen, and now it’s just sitting outside in the sun. The sun heats things, so the plate is getting really warm.
The plate starts to get so warm that you could fry an onion (おん) on it. Who doesn’t love fried onions? That plate sure is warm enough, so start cookin’ ‘em!