1. Scrub cucumbers thoroughly to remove any wax; trim stem and blossom ends, and cut cucumbers crosswise into 1/4-inch-thick slices. Cut onions in half, and slice crosswise into 1/8-inch-thick slices. Place cucumber, onion, and bell pepper in a bowl; toss with salt. Cover and let stand 3 hours at room temperature; drain.
2. Sterilize jars, and prepare lids. While jars are boiling, bring vinegar and next 4 ingredients to a boil in an 8-qt. stainless steel or enameled stockpot, stirring just until sugar dissolves. Add drained cucumber mixture, and cook, stirring often, 7 to 10 minutes or until mixture is thoroughly heated and cucumber peels turn dark green.
3. Ladle hot mixture into hot jars, leaving 1/2-inch headspace. Seal and process jars, processing 10 minutes.
4. Remove jars from water, and let stand, undisturbed, at room temperature 24 hours. To check seals, remove the bands, and press down on the center of each lid. If the lid doesn't move, the jar is sealed. If the lid depresses and pops up again, the jar is not sealed. Store properly sealed jars in a cool, dark place up to 1 year. Refrigerate after opening.
Total time: 4 hours, 10 min., plus 3 weeks standing time