In a small bowl, combine the wasabi powder and mayonnaise. Refrigerate for at least 30 minutes, or until needed.
Cucumber shallot pickles
In a medium bowl, combine the vinegar, water, sugar, salt, peppercorns and ginger. Mix until the sugar and salt dissolve, then add the cucumber and shallot slices.
Refrigerate the mixture for at least 4 hours.
Japanese chicken burger
In a large bowl, combine the chicken, ginger, garlic and soy sauce, then form into 4 patties.
Heat a large non-stick skillet over medium. Add the oil and swirl to coat the bottom of the pan. Season the patties with pepper. Add the patties to the skillet and cook for about 8 minutes per side, or until cooked through. Cover and set aside.
Heat the oven to broil.
Brush the insides of the buns with a small amount of wasabi mayonnaise. Place the buns mayo-side-up on a baking sheet and toast briefly under the broiler.
Brush the buns with more of the mayonnaise. Place a burger on each bun, then top with the cucumber-shallot pickles.