FOR THE SALAD ½ medium red onion, very thinly sliced 2 large English cucumbers, halved lengthwise, seeded and sliced crosswise ¼-inch thick ⅓ cup packed chopped fresh cilantro ½ cup salted peanuts 1 large jalapeño pepper, seeded and minced (or use 1-2 Thai chiles for more heat) ¼ teaspoon salt (optional) FOR THE DRESSING ¼ cup fresh lime juice, from 2-3 limes…