Cut fillet into large chunks. Place fillet, 1 tablespoon tartar sauce, onion, lemon juice, 1/4 teaspoon dill, salt and pepper in a food processor; pulse until blended. Spoon into bowl and stir in bread crumbs. Shape into 3-4 patties and chill for at least 1 hour. Combine remaining tartar sauce, 1/4 teaspoon dill and cucumber in a bowl and chill until ready to serve. Coat salmon patties with cooking spray and either place in a large nonstick skillet or on the grill until done. Serve on bun with cucumber/tartar sauce on top.