Place in a bowl of ice water.
This will reduce the sharpness of the onions.
Meanwhile, peel the grapefruit and cut into thin slices, removing the seeds and reserving any juice reserved.
If you are adventurous, try cutting it into supremes.
Slice the flesh into 1/4 inch slices and toss with any reserved grapefruit juice to prevent browning.
Arrange the grapefruit slices on a large plate.
Layer on the avocado slices.
Top with the red onion slices.
Drizzle with the Pomegranate balsamic.