Boil the barley for 45 minutes until tender, and drain well.
Put all the dressing ingredients, bar the olive oil, into a food processor and blend until smooth. With the motor running, slowly drizzle in the olive oil. Stir the dressing through the barley and mix well.
Pile the barley on a salad platter and garnish generously with olives, parsley, cherry tomatoes, cucumber, spring onions and celery. Top with more rocket leaves.