Rinse 1 cup of dry lentils under cold water to remove dirt or debris. Set aside to drain.

Peel and dice 1.5 lbs of potatoes into 1-inch cubes, and do the same with 2 carrots and 2 celery stalks. Finely dice 1 yellow onion and mince 3 cloves of garlic.

Combine the rinsed lentils, chopped potatoes, carrots, celery, onion, and garlic in the slow cooker. Stir gently.

Pour in 4 cups of vegetable broth and add the undrained diced tomatoes. Stir to combine all ingredients.

Stir in 2 tablespoons of tomato paste, 1 teaspoon of dried thyme, 1 teaspoon of smoked paprika, and season with salt and black pepper to taste.

Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours.

If using, stir in 2 cups of fresh spinach during the last 15-20 minutes of cooking.

Once done, remove the bay leaf, taste, and adjust seasoning if needed. Serve hot, garnished with fresh parsley.