Combine the barley, 3 cups water and a pinch salt in a medium-size saucepan. Bring to a boil, reduce the heat to low and simmer until the barley is tender, about 45 minutes. Drain in a colander and let cool.
Combine the tomatoes, feta, olives, mint, bell pepper and shallots in a bowl. Add the cooled barley.
Whisk together the red wine vinegar and olive oil in a separate small bowl. Season with salt and pepper. Dress the salad and toss. Cover with plastic wrap and place in the refrigerator until ready to serve.
It's best to make the barley salad at least 3 hours ahead of time so the flavors have time to mingle.