It may not be worth investing time learning how to french trim a rack of lamb, or de-boning a whole chicken. We could certainly teach you should you wish, but a butcher can do it for you on the odd occasion you need it. However, dicing an onion properly is a skill no cook should be without. Firstly, once you have learnt, it’s quick. Way quicker than the way you have been doing it. Secondly, it ensures pieces are evenly sized and therefore cook at an even rate; so no more risottos with little burnt bits and big semi raw chunks...
So
Sharpen your knife
Chop the top off the onion
Put this newly flat side on your board and slice through the root
Peel back the skin on both halves, leaving the root in place
Put the cut side on to the board, hold on to the root and slice at regular intervals from root to top
Put one or two slices (depending on the size of the onion) horizontally through the onion towards the root
Then, holding your hand like a claw with the fingers bent underneath, slice the onion across the width into small dice.