1. In a colander, place the cucumber slices one layer at a time, lightly salting each layer. Put a plate weighted with a heavy object on top of the slices, then place the colander over a bowl to catch the water that drains from the cucumbers. Refrigerate.

2. In a saucepan, heat the vinegar, sugar, and red onion over low heat until the sugar dissolves--this shouldn't take more than 2 or 3 minutes. Transfer to a serving bowl, cool, and refrigerate.

3. Remove the cucumbers from the refrigerator, and rinse them under cold water. Pat them dry with paper towels and add to the onion mixture. Refrigerate, covered, for at least 3 more hours.

4. Drain the cucumbers and onions, reserving 5 tablespoons of the liquid. Toss the cucumbers with the reserved liquid and garnish with the chopped fresh dill.