Cut the skin and the white membrane off the oranges. Working over a bowl to catch the juice, cut between the membranes to remove the segments.
Slice the avocados and toss gently with the orange segments. Pile on to serving plates.
Reserve a few whole cardamom pods for decoration. Crush the remaining pods to extract the seeds and pick out and discard the pods. Mix the seeds with the oil, honey, allspice, lemon juice, salt and pepper and reserved orange juice.
Garnish with watercress, spoon the dressing over the top and serve.