Toss the 2 sweet onions and 1 beet with 2 tablespoons kosher salt and let them stand at room temperature for at least 20 minutes. Squeeze as much liquid as you can out of both the beets and onions, then add them to a bowl along with the ¼ cup white vinegar, 1 teaspoon honey, 1 teaspoon kosher salt and a handful cilantro.