Wash the English cucumber thoroughly, then slice it thinly. Place in a mixing bowl, sprinkle with kosher salt, and toss to coat. Let sit for 15 minutes.

In a small bowl, whisk together rice vinegar, honey, toasted sesame oil, and gochugaru until smooth.

Drain excess liquid from cucumbers, add to dressing, and toss to coat evenly.

Transfer to a serving platter and garnish with sliced scallion and toasted sesame seeds if desired.