Aunt Peggy's Cucumber, Tomato and Onion Salad

1 pound cucumbers, (about 2 cucumbers), peeled and thinly sliced 1 pint cherry tomatoes halved 1/2 Vidalia onion, very thinly sliced 2 tablespoons parsley sprigs, chopped fresh 1 tablespoon apple cider vinegar 1 tablespoon olive oil salt and freshly ground black pepper, to taste