Place thinly slice cucumbers in a bowl and sprinkle with salt. Toss well. Allow to sit in the refrigerator while you prepare dressing. (The original recipe says to drain any liquid that comes out of the cucumbers while they set, but we don't do that.).
To prepare dressing: combine the vinegar, water, honey & red pepper flakes in a small saucepan. Bring to a boil, then reduce heat to medium. Cook over medium heat for about 10 minutes, until liquid is reduced to about 1/3 cup. Remove mixture from heat & stir in diced red onion. Let cool to room temperature.
Combine sauce and cucumbers, stirring well to coat. Refrigerate until well chilled or at least an hour.