Prepare the White Barbecue Sauce: Whisk together mayonnaise, vinegar, lemon juice, pepper, garlic powder, onion powder, Worcestershire sauce, salt, and smoked paprika in a medium bowl. Cover and refrigerate until ready to use. Cut cucumbers in half lengthwise; remove seeds with a spoon. Place cucumbers, cut side down, on a cutting board, and smash with the side of a knife. Roughly chop into 1-inch pieces, and place in a large bowl. Season with sugar and 1/2 teaspoon of the salt. Stir to combine, and let stand 15 minutes.  While cucumbers marinate, season salmon fillets evenly with remaining 1 teaspoon salt. Place, skin side down, in a large cast-iron skillet over medium-low. Cook, lightly pressing on salmon every so often with a fish spatula, until skin is golden brown and crispy and salmon is cooked to desired degree of doneness, 10 to 15 minutes. Flip fillets, and remove skillet from heat. Transfer fillets to a large plate, and set aside. Drain cucumbers, and add back to large bowl; add vinegar and oil. Add tomatoes, onion, and feta, and gently toss to combine. Drizzle salmon and salad with White Barbecue Sauce, and top with chives.