Place a large soup pot over medium-high heat with one turn of the pan of EVOO, about 1 tablespoon. Once hot, add the sausage and sauté for 3-4 minutes, breaking it up into small pieces with the back of a spoon or a potato masher as it cooks and browns.
While the sausage is browning, pour the lentils out onto a light-colored plate and sift through them. Discard any small stones -- sometimes you find them sometimes you don't, but better safe than sorry.
To the browned sausage, add the onion, garlic, mushrooms, potato, rosemary, thyme, salt, pepper and the tomato paste. Cook, stirring frequently, for 3-4 minutes.