Make sure to carefully follow each step of the instructions for the best results :
- Slice the vegetables.
Slice the cucumbers into thin rounds or half-moons about 1/4 inch thick. Cut the tomatoes into wedges or dice them into bite-sized pieces. Slice the onion as thinly as possible for the most delicate texture. Place all the vegetables in a large bowl big enough to hold everything plus the dressing with room to toss. - Make the dressing.
In a medium bowl or large measuring jug, whisk together the vinegar, olive oil, water, sugar, salt, pepper, oregano, and garlic powder until the sugar has dissolved completely. Taste the dressing and adjust the balance of sweet, tangy, and salt to your preference before pouring it over the vegetables. A small amount of sugar is key in this dressing — it does not make the salad sweet but instead rounds out the sharp edge of the vinegar. - Combine and toss.
Pour the dressing over the vegetables and toss gently until everything is evenly coated. Scatter the fresh herbs over the top and toss once more. If adding feta and olives, fold them in at this stage. - Marinate and chill.
Cover the bowl and refrigerate for at least 1 hour before serving, tossing once or twice during that time. Most versions recommend a minimum of 1 hour of marinating, though 2 to 4 hours gives the deepest, most developed flavor as the vegetables absorb the dressing fully. - Serve cold.
Serve straight from the refrigerator with a slotted spoon so the excess liquid stays behind. Garnish with extra fresh herbs and a pinch of black pepper right before bringing it to the table.