In a large saucepan bring 2 cups of water to a boil. Stir in barley and reduce heat to medium-low, cover and simmer for 40 to 45 minutes or until tender. Let cool.
In a saucepan bring 1 1/2 cups water to a boil add the rice. Reduce heat to low and simmer, covered for about 20 minutes or until tender. Let cool.
In a large bowl, combine the cooled barley, rice, black beans, kidney beans, corn, onions, red bell pepper and cilantro. Mix well.
To make dressing: In a small bowl, whisk together vinegar, garlic, chili powder, salt, red pepper flakes and black pepper. Whisk in oil and pour over salad and toss well. Transfer to a lettuce-lined bowl to serve.
