Brown the sausage in a skillet over medium heat.
Transfer the browned sausage to the slow cooker.
Add diced onions, garlic, carrots, and celery to the slow cooker.
Stir in the lentils, diced tomatoes, vegetable broth, thyme, and smoked paprika.
Season with salt and pepper, then cover and set the slow cooker.
Check for lentil tenderness toward the end of cooking.
Once cooked, taste and adjust seasoning as necessary.
Serve hot, garnished with fresh parsley.