1. Flake crabmeat with a fork in a medium bowl; stir in 1/4 cup mayonnaise, scallions, soy sauce, 1/2 teaspoon wasabi, and zest. Stir in 2 tablespoons breadcrumbs. Cover with plastic wrap; chill 1 hour.
2. In a medium bowl, whisk together flour, salt, and pepper; set aside. In a small bowl, beat eggs with 1 tablespoon water; set aside. In a shallow bowl, stir together sesame seeds and remaining 1/2 cup breadcrumbs.
3. Form one scant tablespoon crab mixture into a ball; dip in seasoned flour. Flatten into a 3/4-inch high cake about 1 1/4 inches in diameter. Repeat with remaining crab mixture. Dip cakes in egg mixture, then roll in breadcrumb mixture.
4. Heat oil in a large skillet over medium heat until hot but not smoking. Add half the crab cakes; cook, turning once, until golden and crisp on both sides, about 4 minutes. Using a slotted spatula, transfer to paper towel-lined plates to drain. Repeat with remaining cakes, adding more oil if needed. Let cool completely.
5. Meanwhile, stir together remaining 3 tablespoons mayonnaise and 1 1/2 teaspoons wasabi. Using a vegetable peeler, make 24 (2-by-3/4-inch) ribbons from cucumber; fold each ribbon into thirds.
6. Dot each crab cake with 1/2 teaspoon wasabi mayonnaise; top with a slice of cucumber and a slice of ginger.

Yield: 24 servings