Bright-hued sweet vegetable pickles are a welcome change from typical sandwich toppers. Rings of red onion have a refreshing bite.
Cut onions into 1/4-inch-thick slices; transfer to a colander set in a bowl. Toss well with the salt. Refrigerate 1 hour. Rinse well; drain. Pat dry between paper towels.
Bring vinegar, sugar, and spices to a boil in a medium saucepan, stirring. Let cool completely, about 30 minutes.
Add onions; bring to a boil. Transfer onions to a large bowl using a slotted spoon. Let brine cool completely, about 30 minutes; pour over onions. Transfer to airtight containers; refrigerate at least 1 week (pickles will keep 3 weeks more).