In a food processor, blend egg white, green onions, ginger and half of the soy sauce until smooth. Add salmon and panko; blend just until salmon is finely chopped. With wet hands, shape into four ¾-inch-thick patties. Slice zucchini on an angle into thin slices.
Place patties and zucchini on a greased grill over medium-high heat. Close lid and grill, turning once, until zucchini is lightly charred and tender, 4 to 6 minutes, and until patties are cooked through, about 10 minutes.
Meanwhile, in a small bowl, stir wasabi with remaining soy sauce; let stand 1 minute. Whisk in mayonnaise and sesame oil.
Place cooked salmon patties on bun base; top with wasabi mayo and drape zucchini slices overtop.
Per serving: 291 calories, 28 g protein, 10 g fat (2 g saturated fat), 23 g carbohydrates, 4 g fibre, 64 mg cholesterol, 420 mg sodium