Separate the rounds into rings and hold them in ice water until serving time.
In a mixing bowl combine the orange juice, vinegar and olive oil; season to taste with salt and pepper.
Cut the peel and pith away from the oranges and slice them into thin rounds.
Right before serving, make a bed of the arugula leaves, set concentric rounds of oranges on top. Drain onion rings and pat dry and scatter them over the oranges; spoon some of the dressing over the top and serve.