Heat a large soup pot over medium high heat. Add the oil, onion, carrots, tomato and garlic and cook for 3-4 minutes or until fragrant.
Add the harissa, cinnamon, cumin, salt and parsley to the pan. Cook for another 1-2 minutes.
Add the lentils, vegetable stock and water to the pot and bring to a boil. Once it reaches a boil, reduce the heat and simmer for about 40 minutes. Season with salt and pepper to taste.
(Optional) Top each bowl with a tablespoon of Greek yogurt and a sprinkle of fresh parsley.