Thinly slice the cucumber into 1/4-inch rounds and cut the tomatoes into 1-inch wedges, placing them in a large mixing bowl. Thinly shave the red onion to keep the bite mild and pleasant—I recommend using a mandoline or vegetable peeler for paper-thin, even slices that soften slightly as they sit. Finely chop the fresh parsley and set aside.

In a small bowl, whisk together the extra virgin olive oil, apple cider vinegar, dried oregano, granulated sugar, sea salt, and freshly cracked black pepper until the sugar and salt are fully dissolved and the dressing emulsifies slightly. Taste and adjust the seasoning as needed—I find that a touch more vinegar can brighten the salad if your tomatoes are particularly mild.

Pour the vinaigrette from Step 2 over the prepared vegetables in the large bowl and add the chopped parsley. Gently toss everything together until the vegetables are evenly coated and the flavors begin to meld. Cover and refrigerate for at least 20 minutes before serving—this rest time allows the vegetables to soften slightly and absorb the dressing flavors while the onion mellows considerably.