Combine the vinegar and sugar in a microwave-safe bowl
Microwave 1 minute, stir to dissolve sugar & pour over the onion slices to cover.
Refrigerate until ready to use
Salad
Drain the pickled onions, reserving 2 tablespoon of the liquid
Combine cucumber ribbons, and melon balls, pickled onions, and feta in a large bowl.
whisk together olive oil and pickling liquid. Pour over salad and toss gently
Sprinkle with sea salt, and serve immediately
Notes
The salad should be served quite soon after preparing, because the more it sits, the more juices will accumulate from the melon.The melon balls combined should be about 5 cups.This salad is vegan if you omit the feta cheese