Special equipment: A straight-sided 3-quart tall glass bowl or four 16-ounce wide-mouth glass jars with lids
Preheat the oven to 350 degrees F. Spread the walnuts out on a rimmed baking sheet, and bake until golden and toasted, 8 to 10 minutes. Let cool, and roughly chop.
Meanwhile, bring a small saucepan of water to a boil. Add the barley, and simmer until plumped and tender, 20 to 25 minutes. Strain and rinse under cold water. (The barley can be made and refrigerated up to 2 days ahead.)
Use a sharp knife to remove peel and pith from the grapefruits. Cut the grapefruits into pieces, and remove the seeds.
Whisk the vinegar, shallots, mustard, honey, 1/2 teaspoon salt and a few grinds of pepper in a medium bowl. Slowly drizzle in the oil, whisking constantly, until blended into a vinaigrette.
Using a 3-quart straight-sided tall glass bowl for 1 large salad or four 16-ounce wide-mouth glass jars for 4 individual salads, make a first layer with half the mesclun, then add the following in separate layers: the grapefruit, the Brussels sprouts, the barley, the beets, and the remaining mesclun. Sprinkle the walnuts and pomegranate seeds on top.
If making 1 salad, just before serving, transfer it to a large bowl, toss with the vinaigrette and season with salt and pepper. If making 4 salads, add vinaigrette to each jar, season with salt and pepper, cover with the lid and shake to coat.
From Food Network Kitchen