mix whole greek yogurt with mustard powder and fresh tarragon leaves, drizzle tablespoon of olive oil while mixing with fork or small blender to emulsify.
butterfly large prawns. coat with olive oil. grill or broil. do not over cook.
coat asparagus with olive oil. grill. do not over cook.
grill lemon wedges. drizzle warm lemon juice over asparagus and prawns.
lightly toast pumpernickel bread. spread yogurt mixture.
layer with prawn, asparagus, and shave parmigiano-reggiano over.
cover with arugula/watercress.
top with slice of pumpernickel bread. sprinkle tarragon over.