Heat the oil in a large pot and add the veggies (garlic, onion, celery, and carrot). Cook over medium-high heat until golden brown, stirring occasionally.
Add all remaining ingredients except salt and pepper. Stir.
Increase heat and bring to simmer. Cover with a lid, reduce heat to medium-low, and simmer for about 40 minutes or until the lentils are soft.
Finally, add the salt and pepper and stir.
To thicken the soup, use an immersion blender and do 3-4 quick pulses. You could also transfer 1 cup (250 ml) of the soup to a regular blender and blend, then transfer it back into the pot. This step is totally optional.
Serve your lentil soup immediately (I topped my soup with some chopped fresh parsley) with a side of vegetable tempura or veggie stir fry.
Keep the leftovers in an airtight container in the fridge for about 5-7 days or in the freezer for up to 2 months.
Add more or less liquid depending on how thick you want your soup to be.
If you want to reduce the amount of sodium in this recipe, omit the salt and use water instead of vegetable stock. You could also make your own vegetable stock with no salt or buy a low-sodium one.
Lentils do not require it but they can be soaked in order to reduce cooking time. Soaked lentils are also easier to digest.