Peel and dice the onion and garlic. Add the onion, garlic, and olive oil to a large soup pot and sauté over medium heat for about 5 minutes, or until the onion is soft and translucent.
While the onions are cooking, peel and dice the carrots and chop the celery. Once the onions are soft, add the carrots and celery to the pot. Add in the tomato paste and herbs and stir through, cooking until fragrant.
Peel and chop the remaining vegetables and add to the pot along with the soup mix, stirring to combine.
Add stock, water and salt and pepper. Mix through and bring to the boil. Cover and turn the heat down to a low simmer for about 30 minutes or until the barley and lentils are soft.
Add in frozen peas and stir to heat through. Adjust salt and pepper to taste. Serve hot with chopped parsley if desired.