Cucumber Tomato Salad (Mediterranean Salad - Easy Salad Recipe)

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Cucumber Tomato Salad (Mediterranean Salad - Easy Salad Recipe)

 6 Roma tomatoes, diced (about 3 cups diced tomatoes)
 1 large English or hot-house cucumber, diced
 ½ small red onion, thinly sliced, optional
 ¾ bunch parsley, leaves and tender stems chopped
 kosher salt, to taste
 ½ teaspoon black pepper
 1 teaspoon ground Sumac
 2 tablespoon extra virgin olive oil
 2 teaspoon freshly squeezed lemon juice, plus more to taste