Half fill a cooking pot with water and bring to a boil.
Boil the lentils for 10 minutes. Remove from heat and drain lentils in a strainer.
Cut the tomatoes in large pieces and add to a food processor. Blend until smooth. Set aside.
Cut the carrot, pepper and onion into large pieces and add to a food processor along with the garlic cloves. Blend until a smooth paste forms.
In a medium-sized cooking pot heat 3 tablespoons of olive oil over high heat. Add the paste and cook for a minute or two. While stirring with a wooden spoon.
Add the blended tomatoes along with a liter of water.
Season with salt and pepper. Add the bay leaf, the remaining 5 tablespoons of olive oil, and the celery stick finely chopped.
Once soup starts to boil, add the lentils and reduce heat to medium. Simmer until lentils are cooked (time depends on variety of lentils). Usually takes about 40 minutes.
Remove from heat once the lentils are cooked and soup has thickened.