Place the sliced cucumbers in a large bowl and sprinkle with salt. Toss to combine and let sit for 10 minutes to draw out excess moisture.
In a separate bowl, whisk together the sugar, rice vinegar, soy sauce, gochugaru, minced garlic, and sesame oil until the sugar is dissolved.
After 10 minutes, rinse the cucumbers under cold water and drain well. Pat them dry with paper towels.
Add the cucumbers to the bowl with the dressing and toss to coat evenly.
Stir in the sesame seeds and chopped green onions.
Let the salad sit for at least 15 minutes before serving to allow the flavors to meld.