In a medium pot, heat oil over medium heat. Add onions and saute until soft and translucent, about 3-4 minutes. Add barley and cook, stirring frequently, until toasted and golden, about 4-5 minutes more.

Add water, tomato sauce, salt, and pepper, and stir. Bring to a boil, cover, reduce the heat to low, and simmer for 45 minutes or until barley is cooked through and tender. Allow to rest for 5 minutes before serving.