Saute. Heat the olive oil over medium-high heat in a large skillet. Add the shallots, celery, and carrots. Season with salt and saute until the veggies have softened. Turn off the heat.
Load the slow cooker. Transfer the sauteed veggies to the slow cooker along with the pepper, garlic powder, bay leaves, herbs de province, crushed tomatoes, vegetable stock, lentils, and parmesan rind.
Cook. Close the slow cooker and cook on high for 4 hours.
Finishing touches. At the end of the cooking time, remove the lid from the slow cooker. Remove the parmesan rind and stir in the spinach. Stir until the spinach has melted.
Season. Taste the soup and season with additional salt and pepper to taste.
Notes
For those meat lovers, you can add additional flavor by cooking up and adding Italian sausage to this crockpot lentil soup recipe.
Adding more vegetables is a great option. Diced bell peppers and sweet potato would be perfect for cozy soups like this.
Switch out the green lentils for red lentils and create a red lentil soup.
Replace some of the vegetable broth with some coconut milk to turn this into a creamy slow cooker version, but be sure to add it at the end.