Finely chop the onion, garlic, celery and carrot. Dice the red peppers.
Heat the oil in a pan, then gently sauté the onion, celery and carrot for 5 minutes. Add the garlic and red pepper and sauté for another 3-5 minutes.
Meanwhile, rinse the lentils.
When the veggies are tender, add the lentils, the chopped tomatoes and the vegetable stock. Bring to a boil, then reduce the heat and cook, covered, for 25 minutes or so, until the lentils have become soft.
Turn off the heat and add the parsley.
Using a stick blender blitz the soup until you get a textured soup.
Add more stock, if needed and reheat it, if needed.