Heat the olive oil in a soup pot over medium heat. Add the onion, carrot and celery and cook 3 to 4 minutes. Add the garlic and cook 1 minute more. Add the barley, tomatoes, herbs and stock and bring to a gentle simmer. Simmer until the barley is tender, about 30 to 40 minutes. Mix in the peas and heat through. Season with salt and pepper and serve.