Here's a great, healthy side dish with a bit of juiciness and fruity flavor from the grapes and a nice crunch from the pecans. This dish can be prepared up to one day ahead but be sure to garnish with pecans just before serving.
Bring water to a boil in a small saucepan and add ½ teaspoon of the salt. Stir in the barley, reduce heat to low and simmer, covered, until barley is tender but chewy and the water is absorbed, about 45 minutes. Transfer to a medium-sized bowl and fluff with a fork and let cool to room temperature.
In a small bowl, whisk together the oil, vinegar, honey, mustard, remaining salt, and pepper. When the barley is cool, gently stir in the grapes, radicchio, scallion, and tarragon. Drizzle the dressing over the salad and toss thoroughly to combine. Garnish with the pecans.