Preparation Preheat broiler. Line rack of a broiler pan with foil. Put fish skin sides down on foil and sprinkle with pepper and 1/4 teaspoon salt. Whisk together mayonnaise, lemon juice, dill, and chives in a small bowl. Spread evenly over fish, then cover with tomato slices, overlapping slightly, and sprinkle with remaining 1/4 teaspoon salt. Broil fish 3 to 4 inches from heat until just cooked through, 12 to 15 minutes.
Preparation Preheat broiler. Line rack of a broiler pan with foil. Put fish skin sides down on foil and sprinkle with pepper and 1/4 teaspoon salt. Whisk together mayonnaise, lemon juice, dill, and chives in a small bowl. Spread evenly over fish, then cover with tomato slices, overlapping slightly, and sprinkle with remaining 1/4 teaspoon salt. Broil fish 3 to 4 inches from heat until just cooked through, 12 to 15 minutes.