Combine barley and 3cups of water in a saucepan with a pinch of salt. Bring the mixture to a boil, lower the heat and simmer covered until all the water is absorbed and barley is soft yet chewy. Add more water if the pan becomes dry before the barley has finished cooking.
In a small bowl, combine vinegar, olive oil, salt and pepper. Whisk until combined.
Combine slightly cooled barley, chopped veggies (cukes, tomatoes, red onion and corn) and the dressing. Mix well to combine. Taste and adjust the seasoning.
Serve right away or let it sit for a little bit for the flavors to mingle.