1) Bring to a boil in a medium saucepan. Add the barley, oil, and salt. Bring back to a boil, adjust heat to maintain a gentle simmer, cover and cook until tender, about 30 minutes. Remove from the heat and let stand, covered, for 10 minutes more.
2) Meanwhile make the dressing: Whisk the lemon juice, honey, salt, and pepper in a small bowl. Gradually whisk in the oil, starting with a few drops and then adding the rest in a steady stream, to make a smooth dressing.
3) Drain excess liquid from barley, if needed. Transfer to a bowl and toss with the remaining salad ingredients and dressing. Serve warm or at room temperature.