Heat oil in a large frying pan. Add onion and garlic, cooking over a low heat for 4-5 minutes. Stir in tomato paste and cook a further minute. Add carrot and celery and mix through.
Add lentil mix, stock, tomatoes and herbs to the pan. Bring to the boil, reduce heat and simmer for approx. 25 minutes or until lentils are tender.
Stir zucchini and balsamic through mixture and season to taste. Serve with spaghetti and fresh basil.