For burgers:Finely chop half of the salmon and roughly cube the other half.
Combine all salmon in a bowl with scallions, fish sauce, Sriracha, salt and pepper.
Mix until well combined.
Divide into four balls and form into patties.
Chill for at least for an hour.
Heat 4 tablespoons of vegetable oil in a large nonstick sauté pan over medium heat.
Carefully place each patty into the pan.
Cook on each side for approximately 7 minutes on each side, until each side is lightly crispy and golden and patty is cooked through.
Spread a half tablespoon of the wasabi mayo onto each bun, top with a salmon patty.
Top each patty with a half a tablespoon of pickled ginger and a half tablespoon of pickled red onion.
For pickled red onions:Combine all ingredients in a small sauce pan.
Heat to a boil and lower to a simmer.
Simmer for about 10 minutes until liquid is reduced to almost dry.
Remove from heat and allow to cool.
For wasabi mayo:Whisk together the wasabi powder with soy sauce and water to form a paste.
Whisk in mayonnaise.