In a small bowl, whisk together oil, wine vinegar, garlic, oregano, salt, and pepper. Set aside.
Before serving, place tomatoes, cucumber, celery, oregano, and reserved dressing in a bowl and toss to coat all ingredients. Sprinkle with parsley and basil and toss. You can prepare the dressing in advance and put it in an airtight jar. It will keep for up to 4 hours in the refrigerator or be more relaxed.