Begin by preparing the salmon. Slice the salmon fillet into large chunks that will fit the size of your burger buns (about 3-4 inches in width and length). Top the salmon with the salt and olive oil. Use your hands to rub it into the salmon, then set aside.
Next make the mayonnaise sauce/tartar sauce. Add the mayonnaise, garlic, capers, picked, parsley, lemon juice, and black pepper to a mixing bowl and stir to fully combine. Set aside until you are ready to assemble the burgers.
Prepare the tomato and lettuce toppings and set aside until you are ready to assemble the burgers.
To cook the salmon, preheat your BBQ to 350 degrees F. Once hot, add the soaked cedar planks to the grill, close the lid and wait for 7-10 minutes until the planks begin to smoke. Once the planks are smoking, add the salmon to the planks in one even layer and so that they are spaced apart by at least 1 inch. Cover the BBQ and let the salmon cook for 5 minutes.
After 5 minutes, the salmon should turn an opaque orange. Use a silicone brush to spread the birch syrup on top of each piece of salmon. Cover the salmon again and let it cook for another 5-10 minutes, depending on the thickness of the salmon. You will know that the salmon is cooked when you can see it turn orange, white juices are flowing out, and it is firm to the touch.
Remove the salmon and cedar planks from the grill and let cool slightly. Turn off the BBQ and with the remaining heat, toast the burger buns until nice char marks form.
To plate the burger, add about 1 tablespoon of the mayonnaise/tartar sauce to the top and bottom of the burger bun. Next, add the lettuce and tomato, followed by the salmon. Drizzle some extra birch syrup on if desired. Top with the other burger bun and serve immediately. Enjoy!