I don't mean this in a condascending way, but if you chop your onions in a particular manner it's far, far easier, and much quicker to just use a good sharp knife!
If you peel and halve your onion, cutting through from top to tail, make sure you don't cut away the small, slightly tough part at the bottom of the onion - this holds the layers together. All you then do is place the half-onion on the chopping board with the tail-end facing away from you, and finely slice through the onion, from one side to the other, LEAVING a small gap at the top of each slice so that the onion is still in one piece. Then, quarter turn the onion anti-clockwise, slice horizontally through it once or twice depending on the size of the onion, from top to tail (again, ensuring you don't slice all the way). Finally, slice vertically down through the onion, from right to left (working from the cut end to where it's joined) to give a perfect fine dice.
It sounds complicated when it's written down, but it's really easy. Given a little practice you can prepare a whole onion in seconds.