Flake the salmon into a large bowl, then mix in the spring onion, ginger, tamari sauce, lime zest and juice, mashed sweet potato and coriander. Form into 4 burgers, then chill for 20 minutes.
In a small bowl, mix the wasabi with 4 tbsp water, leave for 5 minutes, then stir in the mayonnaise and 1/2 tsp lime juice. Set aside.
You can easily make up the burgers and freeze them, uncooked, for another day.
Put the onion in a small bowl of boiling water, leave for 5 minutes, drain, then mix with the cucumber and chilli. Toss with the sugar, fish sauce and the remaining lime juice.
Heat the oil in a frying pan over a medium heat, then fry the burgers for 3 minutes each side until cooked through. Serve with the wasabi mayo, cucumber salad and roast butternut squash wedges, if you like.
To barbecue, pre-heat your barbecue in the usual way until it reaches the correct temperature. Cook turning once, bearing in mind you may have to adjust the cooking time slightly depending on how hot your barbecue is or how near the heat source the burgers are placed.