Many people, including cooks that work in a professional kitchen, do not know the true technique for mincing a red onion. A lot of people first dice their onion, and then run their knife over the dice in a mincing motion until the onions are a minced, pulverized paste.
The problem is, as you continually mince the onion, the flavor escapes and the onion’s color begins to bleed. If you were to then incorporate that dice into dish with light colors, such as a scallop ceviche, the red color of the onions would bleed into the beautiful white scallop flesh and ruin the look of your dish.
To start, follow the instructions for juilienning an onion. Cut the strips as thin as possible.
Stack your strips of finely julienned onion on top of one another. Using your guide hand technique, cross-cut the juilenned red onions as finely as possible. When done correctly, this will yield a finely diced red onion full of flavor and vibrant with color.