Add the lemon mayo ingredients to a small bowl and stir until combined. Taste and adjust seasonings as needed. Set aside.
Cut the salmon into smaller pieces and add them to a food processor. Pulse a few times until you've got a loosely combined mixture (don't overdo it). Alternatively, you could use a knife to finely chop the fish.
Add the salmon to a bowl along with the lemon juice, Cajun seasoning, salt, garlic powder, parsley, and scallions. Use your hands to gently mix it together.
Add some panko onto a plate (start with only a small amount - you can always add more).
Form the mixture into 4 patties, then coat each of the patties in the panko. The patties will be very delicate and may need to be patted a few times so they stay together. They don't shrink up like beef burgers, so keep the in mind when shaping them.
Add 1-2 tablespoons of oil to a skillet over medium-high heat. Once the pan is hot, cook the salmon patties in 2 batches. I made my burgers fairly thin, so they only took about 3-4 minutes/side.
Assemble burgers with the mayo and toppings. Enjoy!