If necessary, use a fork to fluff up barley and separate pieces. Add tomatoes, cucumbers, and parsley to barley.
In a small bowl or measuring cup, whisk together lemon juice, olive oil, and salt and pepper.
Pour the dressing over the salad and stir to combine and coat everything in the dressing.
Serve immediately if desired, or keep in fridge overnight prior to serving. Feel free to add more lemon juice and olive oil if needed if the barley soaks up some of the dressing.