How to Make It
In a large saucepan, heat the oil over moderately low heat. Add the onion, garlic, and carrots. Cook, stirring occasionally, until the onion is translucent, about 5 minutes.
Add the lentils, water, salt, bay leaf, and thyme. Bring to a boil, reduce the heat, and simmer, partially covered, until the lentils are almost tender, about 20 minutes. Discard the bay leaf.
Stir in the smoked sausage and parsley. Cook until the lentils are just tender but not falling apart and the sausage is warm, about 10 minutes longer.
Because salt slows down the cooking of legumes, the general wisdom is not to add it until they are almost done. Lentils, however, tend to overcook and fall apart all too quickly, so we put the salt in at the outset.