Place the onions in a large bowl; set aside.
In a colander, lightly salt the cucumbers and let drain for about 10 minutes.
Meanwhile, whisk together the ginger, garlic, chives, and vinegar in a small bowl. While whisking, slowly add the oil and whisk until smooth. Add the pepper flakes, and season to taste with salt and pepper.
Add the cucumbers to the onions and toss well. Add the dressing and toss well. Adjust the seasonings. Refrigerate for at least 30 minutes or up to 24 hours before serving. Serve chilled.
Recipe courtesy of Caprial and John Pence, Caprial and John's Kitchen, Ten Speed Press, 2002