Cut the vegetables into medium-sized cubes and finely slice the onion.
Fry the vegetables in a pan with a little olive oil for 10 minutes so they take on some colour. Add the onion and the tomatoes first.
Add the bouquet garni, season with salt and pepper and turn the heat down low.
Cover and leave to simmer for 40 minutes. - Start the polenta at this point.
10 minutes before the end, add the sliced garlic cloves.