Bring barley and broth to a boil in a large saucepan. Reduce heat, and simmer 5 minutes.
While barley cooks, heat oil in a large nonstick skillet over medium-high heat. Add onion; sauté 3 minutes. Add mixed vegetables; sauté 2 minutes. Add vegetable mixture, chicken, salt, thyme, and pepper to barley mixture; simmer 4 minutes.