Cook each grain separately in 2 cups water and 1 teaspoon salt. Cover and bring to a boil. Turn heat to low; simmer quinoa 20 minutes, barley 35 minutes, and wheat berries 55 minutes, or until water is absorbed and grains are tender. Let sit, covered, 15 minutes. Combine grains in a bowl, and let cool. (Grains may be cooked up to 3 days in advance and refrigerated.) Stir in lemon juice and remaining ingredients.