Heat the oil in a large pot (like a Dutch oven) over medium heat. Add the onions, carrot, and ¼ teaspoon of salt and cook, stirring occasionally, until they are soft and starting to smell sweet, about 5 to 7 minutes.
Stir in the garlic, cumin, coriander, black pepper, and turmeric, and cook for 30 seconds.
Stir in the lentils and broth. Increase the heat to high and bring just to a boil. Taste, then adjust with salt (we add between ½ and 1 teaspoon depending on how well-seasoned the broth is).
Reduce the heat to a simmer and cook, partially covered, until the lentils are tender, 35 to 40 minutes.
Uncover the pot, stir in the kale or spinach, and cook, uncovered, another 5 minutes.
Take the soup off the heat and stir in the juice of half a lemon and the fresh herbs. Taste the soup and season with additional salt and/or lemon juice. (I like quite a bit of lemon.)
Serve, or if you prefer the soup blended, use an immersion blender to blend until you achieve your desired consistency. For even more lemon flavor, serve with a few lemon slices.
