In a large pot or Dutch oven, heat the oil over medium heat. Add the onions, carrots, and celery and cook until the vegetables are softened, about 5 minutes.
Add the sausage and cook, breaking it up into small pieces with a wooden spoon, until it’s lightly browned and cooked through, about 5 minutes.
Add the garlic and cook for 1 minute more.
Add the broth, lentils, tomatoes, thyme, salt and pepper and bring to a boil. Reduce the heat to low and simmer until the lentils are tender, about 25 minutes. Taste and adjust the seasoning if necessary.
Stir in the parsley and serve.
Interesting Facts
Lentils are a good source of protein, fiber, and iron.
This soup can be made ahead of time and stored in the refrigerator for up to 5 days.