Rinse the lentils thoroughly and set aside.
Finely chop the onion, carrot, celery, and garlic.
Heat olive oil in a pot over medium heat and sauté the onion and garlic.
Add the carrot and celery and continue sautéing.
Add the lentils and water or vegetable stock.
Season with salt, pepper, and bay leaf.
Simmer over medium heat for 20 minutes until the lentils are cooked.
Cut the tofu into small cubes and add to the soup, simmering for 5 more minutes.
Taste and adjust seasoning as desired before serving.