In a large bowl, combine cucumbers, tomatoes, and red onions. Season with salt and pepper.
In glass canning-type jar, add olive oil, vinegar, tarragon, and sugar. Cover tightly and shake to blend ingredients. Pour over cucumber mixture and toss gently to combine. Cover salad and refrigerate up to an hour.
Garnish with sesame seeds, and parsley, if using.
Choose cucumbers that are thinner as there will be fewer seeds and less likelihood of a woody interior.You can use seedless or English cucumbers for this recipe.