Slice the red onions thinly.
This ensures they absorb all the flavors quickly and evenly.
In a small saucepan, combine vinegar, water, sugar, and salt.
Bring this to a boil over medium-high heat.
Once at a boil, remove from heat.
Let the mixture cool for about 10 minutes.
Squeeze the fresh lime juice and add to the cooled mixture along with the cilantro and optional honey.
Stir well.
Place the sliced onions in a medium bowl.
Pour the liquid over the onions.
Cover and refrigerate for at least 4 hours or up to 2 days before serving.