Prep Vegetables: Dice the onion, carrots, and celery. Mince the garlic. Rinse the lentils thoroughly under cold water, picking out any debris.
Combine Ingredients: Add the rinsed lentils, diced onion, carrots, celery, minced garlic, diced tomatoes (undrained), vegetable broth, bay leaves, dried thyme, cumin, coriander, and smoked paprika to your slow cooker. Stir everything to combine well.
Cook: Cover and cook on low for 6-8 hours or on high for 3-4 hours, or until the lentils are tender. You might wonder, how long does it take to cook lentils in a slow cooker? The exact time depends on your specific appliance and desired tenderness, but always check for softness. One important consideration is, do lentils need to be soaked before slow cooking? Generally, no. Most lentils, especially brown and green, do not require pre-soaking for slow cooker recipes, though rinsing is always a good idea.
Finish and Serve: Remove and discard the bay leaves. Taste the soup and adjust seasoning with salt and black pepper as needed. If the soup is too thick for your preference, add a little more broth or water until desired consistency is reached. Serve hot, garnished with fresh parsley or cilantro if desired.