Precook the barley and make sure to drain it well and place in a large bowl to cool. Also make sure to drain and rinse the can of white beans.
Place the white beans in the large bowl with the cooled barley. Add to them, all of the other salad ingredients; bell pepper, celery, onion, parsley and dill. Mix all of the ingredients until well combined.
Prepare the salad dressing by placing the oil, lemon juice, garlic, vinegar, mustard, salt and pepper, in a small bowl. Whisk until smooth.
Pour the dressing over the tossed barley salad and stir until well combined. Refrigerate the salad until ready to serve.