Toss cucumbers, onion, and salt in colander set over bowl. Let stand 1 hour. Discard any liquid collected in the bowl.
Bring vinegar, sugar, mustard seeds, celery seeds, corriander seeds and turmeric to boil in large saucepan. Reduce heat to low, add cucumbers and onion, and press to submerge in liquid. Cover and cook until cucumbers turn dullish olive-brown, about 5 minutes.
Transfer entire pan contents to glass bowl. Refrigerate, uncovered, at least 2 hours before serving. Pickles can be refrigerated in a clean jar or covered container for 2 weeks.