Place mayonnaise, soy sauce, wasabi and ginger in a bowl, mix well to combine and set aside. Wrap each prawn with a half piece of smoked salmon. Heat the oil in a large skillet set over medium-high heat. Add the prawns and cook 1-2 minutes on each side, or until just cooked through. Serve prawns with wasabi ginger mayonnaise alongside for dipping.
Note: Wasabi powder can be found in the Asian food aisle.