Heat the olive oil in a frying pan and add the onions and garlic and fry for a few minutes, until soft.
Add the carrots, sweet potato and celery. Fry for a few minutes.
Add the dried red lentils and mix well.
Add the chopped tomatoes, passata, herbs, stock (if adding), water and balsamic vinegar. Stir well and bring to the boil.
Turn down the heat and simmer for 1 hour or until everything is soft.
Blend or mash down if servings for a baby.
Serve with pasta and this dish does go lovely with some cheese (if not following a vegan diet).