Add mayonnaise, lemon juice, garlic, basil, salt and pepper to food processor. Pulse until fully mixed. Put basil mayo in a bowl, cover and refrigerate until ready to assemble sandwiches.
To make Six Pepper Bacon:
Preheat oven to 350ºF. Combine brown sugar, six pepper blend and cayenne in a shallow bowl. Dredge each strip of bacon until it is fully covered. Place bacon on a parchment paper lined sheet tray (can also place on wire rack). Bake for 20 minutes or until bacon is brown. Let bacon cool a few minutes, then remove to plate.
To make Salmon:
Heat oil in large nonstick skillet over medium-high heat. Season the salmon fillets with salt and pepper. Sear the fillets in the hot pan until golden and cooked medium, about 3 to 5 minutes per side. Allow salmon to rest while preparing the toppings.
Assemble the sandwiches:
Slather the sourdough toast with a generous amount of the basil mayo. Place the lettuce on the sourdough toast and top with salmon, followed by 2 bacon slices, 2 avocado slices and 2 tomato slices. Top the sandwich. Repeat with remaining ingredients.