This works for any type of onions,

first cut the onion into half vertically.

Lay flat side of the onion on the chopping board, make horizontal cuts towards the roots but not slicing it through.

Then make vertical cuts in the direction of the roots.

Next make cuts opposite to the earlier cuts, and the onions will be cut nicely into dices. The spacing in between the cuts will give you the variations of minced, diced or chopped onions.