Add the lentils to the boiling vegetable stock and simmer for about 25 minutes.
In the meantime, cut the onions and garlic into cubes and sweat them in olive oil, while dicing the tomatoes and adding them. Season everything with salt, pepper and chilli and simmer for about 5 minutes, then remove from the heat.
If necessary, fill the lentils with a little water (approx. 300 - 400 ml) and add the tomato, onion and garlic pan. Simmer everything together for 15 minutes, stir briefly from time to time.
Finally, sprinkle some rosemary into the soup, season again and, if necessary, season with salt, pepper and chilli.