Add barley to about 4 cups of water and bring to a boil. Reduce heat, cover, and simmer until cooked - about an hour. Drain any excess water, rinse with cool water. (Alternate cooking method: soak barley overnight in enough water to cover. Bring to a boil, reduce heat, and simmer about 1/2 hour.)
In a separate pot containing about 4 cups of water, add lentils. Bring to a boil. Reduce heat, cover, and simmer until cooked - about 20 minutes.
Toss barley, lentils, green onions, red pepper, and cilantro in a bowl.
Mix remaining ingredients together, blending well. Stir into lentil-barley mixture, and chill before serving.