1. In a large bowl, combine the sliced cucumbers, onions, and chopped tomatoes. Toss them gently to mix well.
2. In a small bowl, whisk together the apple cider vinegar, olive oil, sugar, salt, pepper, and dried oregano until the sugar is dissolved.
3. Pour the marinade over the vegetables and toss to coat evenly. Let it sit for at least 15 minutes to allow the flavors to meld together.
4. Before serving, add the chopped cilantro (if using) and give it one last toss.
5. Enjoy your salad chilled or at room temperature for the best flavor experience!

As my abuela would say, “Taste as you go.” Adjust the seasoning to your liking, because cooking is as much about intuition as it is about following a recipe.