2) Spread the prawns out in a single layer and roast for 6 to 8 minutes, just until pink, firm and cooked through. Allow to cool for 3 minutes.
3) Meanwhile, make the sauce. In a large bowl, whisk together the mayonnaise, orange zest, orange juice, vinegar, 1/2 tsp salt and 1/2 tsp pepper.
4) When the prawns are cool, add them to the sauce and toss. Add the dill, capers and red onion and toss well. Chill and serve at room temperature.
Cook's note: The flavors will improve if you allow the salad to sit at room temperature for 30 minutes.