Wash cucumber, tomatoes, and red onion. Dice cucumber and tomatoes into half-inch cubes. Soak diced red onion in cold water for 10 minutes, then drain.

In a large mixing bowl, combine diced cucumber, tomatoes, and drained onions. Add chopped cilantro and gently fold together.

Drizzle olive oil and lime juice over vegetables, sprinkle salt and pepper, and toss gently to coat.

Allow salad to rest for 10 minutes at room temperature or refrigerate for 15 minutes before serving.