Heat a heavy soup pot over medium heat. Once hot, pour in the olive oil. Add the onions, carrots, celery, and fennel all at once. Season with salt and pepper and stir. Sauté until vegetables are quite soft, about 10-12 minutes.
Add the garlic, rosemary, lemon zest, and coriander to the pot. Sauté until fragrant, about 1 minute.
Add the lentils and stir. Add 6 cups of vegetable stock and stir once more. Place the lid on top and bring the soup to a boil. Once boiling, lower the heat to a simmer and leave the lid on top, slightly askew so that some steam can escape.
Simmer until the lentils are tender, about 20 minutes.
Place the miso in a bowl and add a couple ladles of hot broth from the soup on top. Use a spoon to "dissolve" the miso into the broth. Pour this mixture into the soup and stir. Stir in the lemon juice and parsley, if using.
Check the soup for seasoning and adjust if necessary (more salt, pepper, lemon juice etc). Enjoy hot with chili oil on top if you like.
Recipe Notes
I say 6-8 cups of vegetable stock because I tend to like this on the much more soupy end with 8 cups of stock. Other folks might prefer a thicker texture. I recommend starting with 6 cups and going from there.
Take your time sautéing the vegetables in the first step. You're building a ton of flavor in this stage.
Make this simple lentil vegetable soup with roughly 12 ingredients and about 35 minutes of cooking time. Miso brings savory depth and lemon perks up the earthy lentils and vegetables. This vegan soup is light and hearty at the same time!