Mix 1 teaspoon each wasabi powder and water; set aside 15 minutes. Halve and pit 3 avocados; scoop the flesh into a large bowl and mash with a fork. Add the juice of 2 limes, 2 tablespoons chopped pickled ginger plus 1 tablespoon brine from the jar, 1 finely chopped seeded jalapeno, 3 thinly sliced scallions, 3 tablespoons chopped cilantro and 1 teaspoon kosher salt. Add the wasabi mixture and stir to combine. Season with salt. Serve with rice crackers.