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 the 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 1/2 teaspoon salt. Cook scallops until golden brown on one 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 1/3 cup chilled pomegranate mixture around the inside edge of each bowl so juice runs to the bottom of the 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.