2) Place the ground spices in a large bowl; add the coriander, spring onions, egg, salt and 1/2 teaspoon of the pepper and mix well. Gently but thoroughly mix in salmon and panko. Shape the mixture into 6 (2cm thick) patties and refrigerate until ready to grill.
3) For the curried mustard mayo, heat the rapeseed oil in a very small nonstick saucepan over a medium heat. Add the ginger and garlic and saute for 2 minutes. Stir in the curry powder and continue to saute for 1 minute. Remove the mixture to a mini food processor; reserve the pan.
4) Add the mayonnaise and mustard to the processor and puree. Remove to a small bowl, stir in the coriander and season, to taste, with sea salt and pepper. Refrigerate until needed.
5) For the orange-apricot glaze, place the preserve, butter, orange juice and cayenne in the reserved saucepan and cook over a medium heat, stirring, until the preserve and butter have melted. Boil the glaze for 2 minutes then remove from the heat and set aside.
6) For the burgers, oil the barbecue grates with rapeseed oil. Grill the burgers over direct heat for 3 minutes, covered if using a gas barbecue. Gently flip the burgers and cook for 3 minutes.
7) Brush the burgers with half the glaze; flip and cook for 1 minute. Brush with the remaining glaze; flip and cook for 1 additional minute or until the burgers are cooked through. Remove.
8) Spray the cut sides of the buns lightly with cooking spray and barbecue cut sides down, along the outer edges of the barbecue, until lightly toasted, about 1 minute.
9) Spread the cut side of the bottom buns with half the mayo mixture; top with half the watercress leaves, a burger, remaining mayo, remaining watercress and tops of buns. Garnish the platter or dinner plates with coriander and watercress sprigs, as desired.