Slice the cucumbers in half lengthwise, then slice into 1/8" slices on the bias. Add 3 tsp sugar and 3 tsp salt, mix well, and let stand 30 minutes.
Combine 1/4 cup sugar and vinegar in a small saucepan. Heat until sugar dissolves, then simmer until reduced to 1/4 cup, about 2 minutes. Set aside to cool.
Squeeze the excess liquid out of the cucumbers and put into a bowl. Add the slightly cooled syrup, and remaining ingredients except Szechwan pepper and salt. Transfer to a serving dish and sprinkle with Szechwan pepper and salt. Serve the same day.