How to Make It
Cook the squash in a medium pot of salted boiling water for 2 minutes. Drain in a colander and run under cold running water until cool. Drain well.
Pack the squash, onions and chiles in a 4-cup container.
Put the vinegar, water, sugar and salt in a small pot and bring to a boil over moderately high heat. Boil, stirring, until sugar and salt are dissolved. Pour the boiling vinegar over the squash mixture. Let cool completely, then seal tightly and refrigerate for 1 day before serving.
Tiny pequin chiles can be found in some Latin American and spice markets. Any small dried chile may be substituted.