Rub a little olive oil all over the chicken breast and sprinkle all over with salt and pepper. Reduce the heat to medium-high and grill the chicken until cooked through, turning once, about 12 minutes. Set aside and keep warm.
Fill a small saucepan with 1/2 cup water, bring to a boil, add some salt, and cook the barley according to package instructions, until tender. Drain and rinse.
Bring the chicken broth and bay leaf to a simmer in a medium saucepan. Add the carrot, celery and zucchini. Cook until just tender, about 5 minutes. Discard the bay leaf.
Place the chicken breast on a cutting board and slice crosswise into thin slices. Spoon the vegetables and barley into serving bowls, then add the hot broth. Lay several slices of chicken over the surface of each bowl.