Place diced cucumbers in a colander and toss with 1 teaspoon salt. Let sit for 15 minutes to draw out excess water. Rinse under cold water and pat dry with paper towels.

In a large bowl, combine the cucumbers, tomatoes, red onion, and parsley.

In a small bowl, whisk together red wine vinegar, Dijon mustard, 1/2 teaspoon salt, and black pepper. Slowly drizzle in olive oil while whisking until emulsified.

Pour the dressing over the salad and toss gently to coat all ingredients.

Let the salad rest at room temperature for 10 minutes before serving to allow flavors to meld.