Bring pomegranate juice to a boil in a small saucepan over medium-high. Boil, undisturbed, until reduced by half, about 7 minutes. Remove from heat. Add sugar and 1 teaspoon salt; stir until dissolved. Transfer to a medium bowl; chill until mixture reaches room temperature, about 30 minutes. Pour lemon juice and orange juice through a fine wire-mesh strainer into pomegranate mixture; stir to combine, and refrigerate until ready to use.
Heat 2 tablespoons oil in a 14-inch nonstick skillet over medium-high. Sprinkle scallops evenly with black pepper and remaining ½ teaspoon salt. Cook scallops until golden brown on 1 side, about 4 minutes. Quickly flip scallops; cook 15 seconds. Divide scallops evenly among 4 shallow bowls; let cool slightly, about 10 minutes.
Arrange pomegranate arils, cucumbers, orange segments, and lemon segments evenly around scallops. Carefully pour ⅓ cup chilled pomegranate mixture around inside edge of each bowl so juice runs to bottom of bowl without covering scallops. Top servings evenly with serrano slices, if using. Drizzle remaining 2 tablespoons oil evenly over scallop mixture; sprinkle with sesame seeds. Garnish with cilantro, and serve with lavash.
