In a medium bowl, mix together the mayo, green onions, lemon juice, salt, pepper and egg. Gently stir in the crab and 1/2 cup of the panko.
Divide the mixture into 4 equal portions, shaping each into a patty about 1 1/2 inches thick.
Spread out remaining panko on a plate. Lightly pat each side of each patty into the panko and set aside. Lightly spray the patties with cooking spray.
Heat the olive oil in a large skillet over medium-low to medium heat. Add the crab cakes and cook about 6 to 7 minutes a side, flipping once, or until each side is nicely browned.
Heat 1 tablespoon oil in a large nonstick skillet over medium heat. Add 6 crab cakes; cook 7 to 8 minutes on each side or until browned. Remove crab cakes from pan; keep warm while you prepare the aioli.
For the aioli: In a blender or a mixing cup for an immersion blender, add the egg, sriracha, and salt. While the blade is running, slowly drizzle in the oil; continue blending until the mixture is emulsified.
To serve: Serve crab cakes warm drizzled with a little of the aioli. Garnish with green onion and lemon slices. Offer remaining aioli on the side.