Place the dried wakame in a large bowl and cover with cold water. Let soak 8–10 minutes until rehydrated and tender. Times vary by brand—seaweed should expand and soften but not be slimy.

Drain the wakame in a fine-mesh sieve and gently squeeze out excess water. If pieces are large, chop into 1–2 inch lengths with kitchen scissors or a knife. Transfer to a mixing bowl.

Dressing

In a small bowl or jar, combine soy sauce, rice vinegar, mirin, sesame oil, sugar, grated ginger, minced garlic, and chili flakes (if using). Whisk or shake vigorously until sugar dissolves and dressing is uniform.

Taste the dressing and adjust: add a little more rice vinegar for brightness, more soy for saltiness, or a touch more sugar or mirin if too sharp. If desired, stir in lime juice for extra acidity.

Assemble & Finish

Combine

Add the sliced cucumber, julienned carrot, red pepper (if using), and most of the scallions to the bowl with the drained wakame. Pour the dressing over the vegetables and seaweed.

Toss

Gently toss everything together with tongs or salad spoons until the seaweed and vegetables are evenly coated. Let sit 5–10 minutes to allow flavors to meld; toss once more before serving.

Garnish & Serve

Transfer the salad to a serving bowl, sprinkle toasted sesame seeds and remaining scallions on top. Serve chilled or at cool room temperature as a side or starter. Keeps well covered in the refrigerator for up to 2 days; drain any excess liquid before serving.