In a small bowl, combine all the ingredients. Keep in the refrigerator until ready to serve.
Preheat the grill, setting the burners to high. Oil the grate.
In another bowl, combine all the ingredients until smooth. Add bread crumbs if the mixture is too soft. Season with salt and pepper. Shape into 6 patties.
Adjust the burners to medium heat. Grill the patties for 3 to 4 minutes on each side or until the salmon is cooked through. Toast the buns.
Spread the caper mayonnaise on the inside of the toasted buns. Place the lettuce and then the patties on the bottom halves of the buns. Garnish with cucumber slices and cover with the top halves of the buns.