In a large pot, wash and rinse the barley and lentils. Fill pot with a lot of water, and bring to a boil. Once boiling, reduce the heat and boil until cooked - 45 minutes to an hour.
Drain and rinse with cool water.
Transfer to a salad bowl and toss with the onions/chives.
Combine all the dressing ingredients, then add to the lentil-barley-onion mixture, stirring until well combined.