Cut the top and bottom top and bottom off of the red onion and peel away any tough outer layers. Use a mandoline or a sharp knife to slice the red onions into thin strips.
Place the cut onion in a bowl (with a sliced jalapeno if desired) and sprinkle with sugar and salt.
Mix it around with your hands massaging in the salt and sugar to the onion slices and allow it to sit for 5 minutes.
After 5 minutes add lime juice, vinegar, and water. Place in the fridge for at least 1 hour or up to 2 weeks before serving.
Notes
Follow directions carefully if using a mandoline to slice your onions. Be sure to keep your fingers away from the blade.
The jalapenos are optional, but add a nice flavor to the pickled onions. You can leave the seeds on the jalapenos for spicer pickles or remove them for less heat.