In a medium bowl, toss together the cucumbers, red onion and tomato. Gently stir in the mayonnaise, vinegar, salt and pepper until coated. Cover and refrigerate for at least 1 hour before serving.
Whisk together the vinegar, olive oil, Italian seasoning, oregano, rosemary, salt and pepper, garlic, basil and marjoram.
Pour dressing over vegetables, toss and chill for at least 4 hours. Drain by serving with a slotted spoon.