For the best Thai cucumber salad, toss the sliced cucumber in salt and press out excess water. Make sure that the sweet chili sauce has cooled before stirring in the lime juice.
Split the cucumber into halves vertically, scoop out the seeds with a spoon and discard. Thinly slice the cucumber halves.
Place the sliced cucumber in a bowl and sprinkle with salt. Toss well. Cover the bowl and chill in the fridge for 15 minutes. The salt will draw out water from the cucumber to prevent your salad from turning soupy. So, please don't skip this step.
Peel, halve and thinly slice the onion.
Make the dressing by whisking together the sweet chili sauce and lime juice.
Roughly chop the roasted peanuts.
Take the cucumber out of the fridge and transfer to a colander. With your hands, squeeze out as much of the water as you can without tearing the cucumber slices.
Transfer the squeezed cucumber to a bowl and toss with the onion slices.
Drizzle in two to three tablespoons of the dressing and toss lightly but thoroughly. Taste and, if you feel that mixture needs more flavor, add the rest of the dressing.
Transfer the salad into bowls. Sprinkle with peanuts and cilantro.