Brown the sliced sausage in a skillet over medium heat for about 5 minutes. This step adds flavor before the ingredients go into the slow cooker.
Add the browned sausage, rinsed lentils, diced onion, carrots, celery, and minced garlic to the slow cooker.
Pour in the diced tomatoes with their juices and the chicken broth.
Stir in the dried thyme, smoked paprika, salt, and black pepper.
Cover and cook on low for 6 to 7 hours until the lentils are tender and the stew has thickened.
Stir the stew once more before serving to check the seasoning.