Add the chopped onions, garlic, leeks and celery to a pot with all the herbs and an inch or two of cold water and cook until soft for about 5 minutes.
Add the Puy lentils and half the stock to the pot. Cover and cook for 20 - 25 minutes until the lentils are cooked. Add more stock if necessary throughout the cooking.
Add the raw red pepper and corn to the pot and stir together, then it's ready to serve.