Slice the cucumbers in half lengthwise, then cut each half into half-moon slices about 1/4 inch thick. Put them in a medium bowl and toss with the kosher salt. Let the cucumbers sit for 10 to 15 minutes. They will release a noticeable amount of liquid during this time.

Drain the cucumbers in a colander. Use your hands or press firmly with a clean towel to squeeze out as much water as possible. This step matters. Excess moisture will dilute the brine and make the salad taste flat. The cucumbers should feel damp but not wet and dripping.

In a small bowl, whisk together the gochugaru, rice vinegar, sesame oil, fish sauce, and sugar until the sugar dissolves. Add the minced garlic and stir to combine. Taste the brine. It should be spicy, tangy, and savory. If you want more heat, add another 1/2 teaspoon of gochugaru. Keep in mind the spice will build as the salad sits.

Add the drained cucumbers and sliced green onions to the bowl with the brine. Toss everything together with a spoon or clean hands until every piece is evenly coated. The cucumbers should turn a vibrant reddish-orange color from the gochugaru.

Transfer to an airtight container and refrigerate for at least 1 hour. If you can wait 3 to 4 hours, the garlic mellows slightly and the cucumber soaks up more of the spice. The salad is genuinely better the longer it sits, up to 24 hours.

When ready to serve, taste once more and adjust with a tiny splash of rice vinegar if you want more brightness or a pinch of salt if needed. Spoon into a bowl and top with toasted sesame seeds. Serve cold alongside rice, grilled meat, or anything that benefits from a punchy, cooling contrast.