Sauté the onions and garlic in a few sprays of low calorie cooking spray, until they start to soften.
When the onion starts to soften, add the meatballs, carrots and celery and continue to cook until they start to brown.
Add the courgettes and mushrooms, and allow to cook for a few minutes.
Add the herbs, tomato puree and chopped tomatoes. Stir well.
Mix the stock cube in about 100ml of boiling water, then add that to the pan. Mix well, then bring to the boil.
Reduce the heat, cover with a lid and simmer for 15 - 20 minutes stirring occasionally.
Serve 6 meatballs per portion with spaghetti, pasta, rice slimming chips or whatever you fancy.