Place the dried wakame in a large bowl and cover with cold water. Let soak 8–10 minutes until tender and expanded. Drain in a fine sieve, pressing gently to remove excess water. Trim any large tough stems and chop into bite-sized pieces if needed. Squeeze lightly to remove excess moisture and transfer to a mixing bowl.

Prepare vegetables

While seaweed soaks, julienne the cucumber and carrot into thin matchsticks. Thinly slice the scallions. Pat cucumber dry with a paper towel to remove excess water so the dressing won't be diluted. Add cucumber, carrot, and scallions to the bowl with the drained seaweed.

Dressing

Mix dressing

In a small bowl or jar, combine rice vinegar, soy sauce, sesame oil, sugar (or honey), mirin (if using), lime juice, grated ginger, minced garlic, and chili oil (if using). Whisk vigorously until sugar dissolves and the dressing is uniform. Taste and adjust: add a little more vinegar for tang, more sugar for sweetness, or more soy for saltiness.

Assemble & Finish

Pour the dressing over the seaweed and vegetables. Toss gently but thoroughly to coat all ingredients. Let sit 5–10 minutes so flavors meld; toss once more before serving.

Season with salt and black pepper to taste (remember soy adds salt). Sprinkle toasted sesame seeds and optional sliced chili or chili flakes on top. If desired, finish with a small extra drizzle of toasted sesame oil for aroma.

Serve chilled or at cool room temperature. Store leftovers in an airtight container in the refrigerator for up to 2 days; note the cucumber will soften over time.