Wash the cucumbers thoroughly. Using a sharp knife or mandoline, thinly slice the cucumbers into uniform rounds or half-moons, about 1/8-inch thick. Place the sliced cucumbers in a large mixing bowl and toss them with 1 teaspoon of salt. Let them sit for 10-15 minutes at room temperature; this process draws out excess water and helps them retain a crisp texture.

After 10-15 minutes, the cucumbers will have released a significant amount of liquid. Transfer the cucumbers to a colander and gently squeeze out as much excess water as possible. You can use your hands or press them against the colander. This step is crucial for preventing a watery salad. For best results, lightly pat them dry with paper towels.

In a small mixing bowl, combine the gochugaru (Korean chili flakes), soy sauce, rice vinegar, toasted sesame oil, granulated sugar, minced garlic, and 1 tablespoon of toasted sesame seeds. Whisk all the ingredients together thoroughly until the sugar is dissolved and the dressing is well combined. Taste and adjust sweetness or spiciness if desired.

Return the drained and patted-dry cucumbers to the large mixing bowl. Pour the prepared dressing over the cucumbers. Add the thinly sliced fresh chives or green onions.

Gently toss all the ingredients together using your hands (wearing gloves is recommended due to gochugaru) or a spatula, ensuring the cucumbers are evenly coated with the vibrant dressing. Serve immediately for optimal crispness, or chill in the refrigerator for 15-30 minutes for flavors to meld further. Garnish with a sprinkle of extra toasted sesame seeds before serving.