For the salmon burgers, place the salmon, garlic, ginger, soy sauce, lemon zest, lemongrass, and green onions in a food processor and pulse until just combined. Add the egg white, Panko crumbs, and salt and pepper and pulse until combined. (If you don’t have a food processor, finely chop the salmon and then combine all ingredients in a large bowl until combined.)
Form the salmon mixture into four patties and refrigerate, covered in plastic wrap, for 15 minutes.
For the avocado wasabi sauce, thoroughly clean out the food processor and add the avocado, lime juice, wasabi paste, jalapeno, and a dash of soy sauce. Process until smooth. (Add more soy or lime if desired.) Season with salt and pepper to taste. Chill until ready to use.
Heat a grill pan over medium-high heat, and brush with the vegetable oil. Grill the salmon burgers until medium, about 3 minutes per side. Squeeze the lemon wedges over the burgers.
Serve on brioche buns with a dollop of avocado wasabi sauce and thinly sliced cucumber (and some arugula and red onion if you want).