Prep. In a medium bowl, whisk the sugar, salt, vinegar, and water together until the dry ingredients are dissolved.
Chop the scallions on an angle starting from the white bulb up the stem about two inches into the green stems. Squish them a bit to separate them into rings. Add to the bowl.
Cut the jalapeño in half lengthwise. Scrape out the seeds. If you don't want it too hot, cut out the white ribs. Like heat? Leave the ribs in there. Thinly slice the jalapeño and add to the bowl.
Peel the cucumbers and run the tines of a fork lightly along the exterior flesh so that it makes scratches in the surface. Scoring the cucumber like this is not necessary, it just makes it look cool. Cut the cucumber in half lengthwise and scoop out the seeds with a teaspoon. Cut the cucumber into 1/8-inch (3.2 mm) slices. Add to the bowl. Add the basil. If you are using cilantro, add it now.
Marinate. Stir everything, coating the ingredients with the dressing, then cover and let it marinate in the refrigerator for at least 30 minutes or up to 2 hours.
Serve. Serve chilled. If you plan to use chopped peanuts as a topping, add them at the last minute so they don't get soggy.