1. Preheat oven to 200°. Combine first 8 ingredients in a medium bowl. Fold in crabmeat. Shape crab mixture into 20 to 24 (2-inch) patties; chill 1 hour.
2. Melt butter with oil in a large skillet over medium-high heat; cook crab cakes, in 2 batches, 2 to 4 minutes on each side or until golden. Place on baking sheet, and transfer to oven to keep warm.
3. Whisk together mayonnaise, wasabi, and lime zest; season mixture with salt and pepper. Dollop crab cakes with wasabi mayonnaise. Sprinkle with green onion.