1 tablespoon olive oil
1 large yellow onion, chopped
2 medium carrots, chopped
2 medium celery ribs, chopped
4 cloves garlic, minced
1 pound sweet or hot turkey sausage, casings removed
1 pound lentils, sorted, rinsed, and drained
1 quart low sodium chicken broth
1 quart water, plus more as needed
1/2 teaspoon dried rosemary
1 teaspoon kosher salt
1/2 teaspoon crushed hot red pepper
1 (14.5-ounce) can no-salt-added diced tomatoes in juice, undrained
2 cups whole-wheat rotini or other tubular pasta
Heat the oil in 1 large pot over medium heat. Add the onion, carrots, celery, and garlic and cook, stirring occasionally, until softened, about 5 minutes. Add the turkey sausage and cook, stirring occasionally and breaking up the meat with the side of a wooden spoon, until the sausage loses its raw look, about 6 minutes.
Stir in the lentils, broth, water. rosemary, salt, and hot pepper and bring to a boil over high heat. Reduce the heat and simmer, stirring occasionally, until the lentils are softened, about 45 minutes. Add the tomatoes and their juice and simmer until the lentils are tender, adding more hot water as needed to barely cover the lentils, about an additional 45 minutes.
Add enough hot water to cover the lentils by 1/2 inch and bring to a simmer. Stir in the pasta and cook until the pasta is very tender, about 15 minutes. Ladle into soup bowls and serve hot.