Whisk together the oil, orange juice, mustard and some freshly ground pepper in a small bowl to form a vinaigrette.
Peel the oranges and remove all the white pith with a sharp knife. Cut in slices and then halve. Blanch the asparagus for 1 minute in boiling water in a large saucepan then refresh under cold running water.
Arrange the salad leaves on 4 plates then top with the asparagus spears, the orange slices and the avocado slices. Drizzle with the vinaigrette and add a further grinding of pepper.