Clean, chop, wash, spin dry the radicchio and place on serving plates. Halve, peel and slice the avocados. Arrange the slices as a rondelle on the radicchio. Peel the onion, cut into very thin rings and place them on the salad. Add a few black olives to each plate.
For the salad sauce, whisk the olive oil with freshly squeezed orange juice, salt and pepper. Drizzle over the salad just before serving.