Whisk Egg, Mayo, mustard, pepper, salt and cayenne together until combined. Stir in scallion. Add crab and panko, stir to combine.
Form the mixture into 4 ½ inch thick patties.
Heat the oil in a large nonstick skillet over high heat until simmering. Add crab cakes and cook 4-5 mins per side only flipping once. Garnish with lemon wedges.