How to Make It
Using a pair of kitchen scissors, cut down the middle of the backs of the prawn shells. Leave the shells on and pull out the central vein.
Fill a large bowl with ice water. Using a mandolin-style slicer, and holding the vegetables lengthwise, very thinly slice the asparagus tips, carrots, turnips, radishes, red onion and cucumber directly into the ice water bath. Add the celery, parsley and tarragon leaves and refrigerate until the vegetables are crisp, at least 30 minutes or up to 1 hour.
Light a grill. In a small bowl, mix the 1/2 cup of olive oil with the lemon juice and zest. Season the dressing with salt and pepper. Drain the vegetables and herbs and dry thoroughly in a salad spinner. Wrap the vegetables and herbs in paper towels and keep in the refrigerator.
Brush the prawns with olive oil and season with salt and pepper. Grill the prawns over a medium-hot fire until just cooked through, about 3 minutes per side. Transfer to a platter and let rest for 5 minutes.
In a large bowl, toss the vegetables and herbs with half of the dressing. Arrange the vegetables on 8 plates. Halve each prawn lengthwise through the shell. Top each salad with 3 prawn halves, drizzle with the remaining dressing and serve.