1. Place the cucumber slices in a colander. Sprinkle the slices with ½ teaspoon of kosher salt; toss to combine. Place the onion slices in a medium bowl. Add the apple cider vinegar to the onions; toss to coat. Let the cucumbers and the onions sit for 30 minutes. 2. After 30 minutes, squeeze the cucumbers to remove any excess moisture. Place the cucumbers in the bowl with the onions. 3. Add the tomato, mayonnaise, and fresh herbs to the bowl with the onion/cuke mixture. Stir to combine, adding more mayonnaise if necessary. Refrigerate the salad for at least one hour before serving. Taste for seasoning, adding more salt and a lot of freshly ground black pepper.