Whisk together the olive oil, red wine vinegar, oregano, salt, and some freshly cracked pepper in a bowl, or combine them in a jar and shake until mixed. Set the dressing aside to allow the flavors to blend. Thinly slice* the tomato, cucumber, and red onion. Place them in a large bowl. Pour the dressing over the sliced vegetables and toss to coat. Serve immediately, or refrigerate until ready to eat. The onions will become more mild as they marinate in the dressing.
