This video shows you how to dice a yellow onion quickly and easily.
You must start with removing the stem by cutting a small portion of the onion. Now you have to cut the onion in half, leaving the root on. Then you position a half with the root away from you and make deep cuts through the whole onion in a star burst pattern (the cuts at the sides are at an angle), but you don't cut all the way to the root, so the onion doesn't break into pieces. Then you position the onion with the root to your side and make cuts towards the root, removing it at the end. At this point, the onion is fully diced.