Prepare the dressing by whisking together all the ingredients for it in a small mixing bowl until smooth. Cover and chill until serving point.
Cook the eggs in a saucepan of boiling water for 12 minutes. Strain and run under cold water for 2 minutes until cool enough to handle.
Cook the asparagus spears in a large saucepan of salted, boiling water for 2 minutes. Strain and run under cold water for 1 minute. Set to one side.
Heat the olive oil in a large frying pan set over a moderate heat until hot. Season the prawns then sauté for 3-4 minutes until pink and tender. Remove from the heat and set to one side.
Tear the lettuce leaves roughly and arrange in serving bowls. Top with cherry tomato halves and a few asparagus spears. Peel and cut the eggs in half. Arrange them on top then spoon over some of the flaked crab.
Tuck the prawns into the salad, then spoon some of the dressing on top. Serve immediately.