Peel the oranges, cut off the pith and slice horizontally.
If you are using a whole pomegranate, cut it in half and hit each half with a wooden spoon to dislodge the seeds.
Slice the onion very finely into rings or half moons.
Arrange the orange slices on a plate. Scatter the onions, pomegranate seeds and olives on top of the orange slices.
Squeeze over the lemon juice and drizzle with olive oil. Season. Serve.