Cook the barley in a medium pot in plenty of salted water until tender but still chewy, 20 to 30 minutes. Drain and cool.
In a food processor, combine the tahini, scallions, jalapeno, garlic, vinegar and oil. Season with salt and pepper. Process until you have a smooth, thick green dressing. If the mixture is too thick, add 1/4 to 1/2 cup of water to thin to about the consistency of pancake batter.
Combine the vinaigrette and cooked barley and mix to thoroughly coat the barley. You may not use all the vinaigrette. Set up two serving bowls. Evenly divide the barley between the two bowls. Top each with the olives, tomatoes and capers. Season with a pinch more salt and garnish with the cilantro.