Prep the ingredients per the instructions above.
In a bowl, mix together the ingredients for the aioli. Season with salt and pepper to taste.
Preheat a the oven broiler on low or medium.
Cook the salmon: Lightly grease a foil lined baking sheet with nonstick spray and place the salmon on. Season the salmon with salt and pepper. Place under the broiler to an internal temperature of 125 °F (51 °C). While the salmon is cooking, toast the buns.
Once the salmon is cooked, set aside to rest for 3 to 5 minutes.
Make the sandwich: Spread aioli on the inside of both halves of the toasted buns. Layer with lettuce, tomato, salmon, and onion.
Mix together the sparkling water and lemon. Serve over ice if desired.
Serve: Enjoy the sandwich with chips, pickle, and lemon sparkling water.