Step 1

Scrub loofah and peel only the ridges, then cut diagonally into 1/2-inch-thick slices. Toss loofah with kosher salt in a bowl, then cover with ice and let stand 2 hours. Drain and remove any unmelted ice.

Step 2

Bring vinegar, water, sugar, mustard seeds, celery seeds, and turmeric to a boil in a 1-quart nonreactive saucepan, stirring until sugar is dissolved. Add loofah and onion, then reduce heat and simmer, uncovered, 5 minutes.

Step 3

Transfer pickles with liquid to a 1-quart heatproof glass or ceramic bowl and cool to room temperature. Chill, covered, at least 2 days (for flavors to develop) and up to 1 month.