Put cucumbers and carrots into a colander and toss with salt. Let sit and drain in the sink for 30 minutes.
While cucumbers and carrots are draining, peel onion and slice into thin half-moons.
After 30 minutes, use paper towels or a clean kitchen towel to blot cucumbers and carrots dry and press out any excess liquid.
Pour carrots and cucumbers into a large bowl and stir in red onion slices.
Then stir in vinegar, sugar, and sesame oil.
Cover and put in the refrigerator to chill for 2 hours, stirring occasionally.
Stir in sesame seeds before serving.
Notes
This Carrot Cucumber Salad is best eaten the same day you make it but will keep for 1-2 days in the refrigerator. It will lose some of its crunch, but is still tasty. Depending on how long the salad has been sitting in the refrigerator, it may have more or less liquid at the bottom of the bowl. If there is a lot of excess liquid, you can use a slotted spoon to serve, or drain the salad into a colander before putting into a serving bowl. I like the round discs of cucumber and carrot in this salad, but you can grate the carrots instead. Or you could spiralize either the carrots or the cucumbers or both!