Wash the Kirby cucumbers under cold water and then slice into 1/3-inch rounds, about as thick as an Oreo. Peel the onion, cut in half lengthwise, and slice into semicircles the same width as the cukes. Toss the onions and the cucumbers in a bowl with the salt and let sit for 1 hour. Rinse well in a colander, drain, and place in a nonreactive bowl. Tear up the celery leaves and add to the mix, then set aside.
In a saucepan, combine the pepper flakes, fenugreek, tumeric, mustard seeds, the allspice berries, vinegar, 1/2 cup water, the sugar, and maple syrup. Bring to a rapid boil and then pour over the cucumbers. Leave them uncovered for 2 hours and then refrigerate. When they reach fridge temperature, cover with plastic wrap. Done. But they'll be at their best a day or two later. They'll keep in the refrigerator for about 10 days.
You can use store-bought pickling spice instead of the allspice and preceding four ingredients, and you'll end up with good pickles, but not these pickles. And these pickles are better.