In a mixing bowl, combine the sliced cucumber, diced tomatoes, and red onion.
Drizzle the olive oil and red wine vinegar over the vegetables, then sprinkle with salt and pepper to taste.
Add the fresh herbs if using, and gently toss the ingredients until evenly coated.
Cover the bowl and place in the refrigerator for a minimum of 20 minutes to allow the flavors to blend.
Serve chilled as a crisp, flavorful side.