Cut the large English cucumbers in half lengthwise and scoop out the seeds. Slice them into 1/4 inch thick pieces and place in a large bowl.

In a small saucepan, heat sugar, salt, rice vinegar, and red wine vinegar over medium heat until dissolved. Remove from heat and let cool.

Add matchstick chopped carrots and thinly sliced red onion to the cucumber slices in the bowl. Mix in chopped cilantro if using.

Pour the cooled dressing over the vegetables, add sweet chili sauce and lime juice. Toss everything together until well-coated.

Cover and refrigerate for at least 1 hour to marinate before serving.