Set oven rack in the lowest position and heat oven to 450° F. Brush a rimmed baking sheet with the oil.
In a medium bowl, combine the crab, bread crumbs, scallion whites, egg, sesame seeds, lime zest, 2 tablespoons of the mayonnaise, and ¾ teaspoon salt. Form the mixture into 20 patties (about 1 tablespoon each) and place on the prepared baking sheet. Bake until golden and cooked through, 3 to 4 minutes per side.
Meanwhile, in a small bowl, mix together the Sriracha and the remaining 3 tablespoons of mayonnaise. Dividing evenly, spoon onto the crab cakes; sprinkle with the scallion greens and additional sesame seeds. Serve with the lime wedges.