Combine apple cider vinegar, fresh oregano, sugar, salt and pepper, in small bowl and whisk until well combined.
Pour dressing over cucumbers and toss to combine. Cover the salad and place in the fridge for at least 30 minutes, but up to 3 hours ahead for the flavors to really meld.
Before serving, add the feta cheese and toss one more time.
Enjoy!
Notes
If you want the sugar to completely dissolve, you will need to heat the vinegar and whisk the sugar until it's dissolved.