Soak seaweed in warm water to cover, 5 minutes. Drain, then squeeze out excess water. If wakame is uncut, cut into 1/2-inch-wide strips. Stir together vinegar, soy sauce, sesame oil, sugar, ginger, and garlic in a bowl until sugar is dissolved. Cut apple into 1/4-inch dice and add to dressing with seaweed, scallions, and cilantro, tossing to combine well. Sprinkle salad with sesame seeds.