Slice the cucumbers thinly into rounds, about 1/8-inch thick.
Place the sliced cucumbers in a colander set over a bowl or in the sink, and toss with the kosher salt.
Let the cucumbers sit for 10 minutes to draw out excess moisture.
While the cucumbers rest, whisk together the minced garlic, rice vinegar, soy sauce, sesame oil, sugar, and gochugaru in a small bowl.
Rinse the salted cucumbers under cold water to remove excess salt, then pat them dry with a clean kitchen towel or paper towels.
Transfer the dried cucumbers to a large mixing bowl.
Pour the dressing over the cucumbers and toss gently to coat evenly.
Add the toasted sesame seeds and sliced green onions, and toss again.
Let the salad marinate at room temperature for 10 minutes before serving to allow flavors to blend.
Taste and adjust seasoning if needed, then serve immediately or chill until ready to eat.