To make the herb dressing, place chives, parsley, mint, oil, vinegar and yoghurt in a bowl and mix to combine.
Preheat oven to 200ºC.
Thinly slice baguette, finely grate parmesan onto a tray. Brush baguette on both sides liberally with oil and coat in parmesan. Bake in 200ºC oven for 5 min or until golden.
Place quail eggs in boiling water for 2 ½ minutes, remove and place in iced water. Peel and return to iced water until completely cooled.
Arrange watercress on a large platter top with asparagus, quail eggs, prawns and crostini. Drizzle with dressing to serve.