In a large Dutch oven or other heavy pot, heat oil over medium. Add carrots, onion, and garlic and cook, stirring occasionally, until beginning to soften, about 6 minutes. Add mushrooms and season with salt and pepper. Cook until mushrooms are softened and golden brown at edges, about 8 minutes.
Add thyme, lentils, and 7 cups water; bring to a boil. Reduce heat, partially cover, and simmer until lentils are tender, about 25 minutes. Stir in soy sauce and season to taste with salt and pepper. Serve soup topped with yogurt.
Made this tonight for dinner and it was a little bland. Perhaps I was light on the salt? My soup did not look anything like the pic! It never really thickened as much as the pic suggested it would. Husband was not a fan so now I have an entire pot to finish on my own!
I only tried this recipe because my husband loves lentils and mushrooms - I am not the type of person who considers anything with soup in the title to be dinner material. This is truly addictive, especially wtih a little sea salt on top (not to mention filling and guilt-free).