Heat oil in a large saucepan over medium-high heat. Add onion and garlic; sauté 2 minutes. Add barley; cook 1 minute. Stir in Homemade Chicken Stock; bring to a boil. Cover, reduce heat, and simmer 30 minutes. Stir in zucchini, tomatoes, salt, and pepper; cover and cook 5 minutes. Ladle 1 cup barley mixture into each of 4 bowls. Top each serving with 1 1/2 teaspoons feta and parsley, if desired.