1 cup (any) lentils, rinsed
4 cups water
4 cups vegetable stock or chicken broth
3 tablespoons olive oil, plus more for serving (optional)
1 large onion, finely chopped
Pinch of crushed red pepper
1 bunch green Swiss or rainbow chard, ribs and leaves separated, leaves coarsely chopped
3 small carrots
1/3 cup fresh lemon juice
In a medium saucepan, combine the lentils with the water, stock and 1 1/2 teaspoons of salt and bring to a boil. Cover partially and cook over moderately low heat until the lentils are barely tender, about 25 minutes.
Meanwhile, heat the 3 tablespoons of olive oil in a large skillet. Add the onion, crushed pepper and a pinch of salt and cook over moderately high heat, stirring occasionally, until the onion is lightly browned, 7 to 8 minutes. Add the garlic and cilantro and cook for 1 minute. Gradually add the chard leaves and cook, stirring occasionally, until wilted, about 3 minutes.
Add the chard to the lentils, cover partially, and simmer until thickened, about 15 minutes. Stir in the lemon juice and season with salt and pepper. Ladle the soup into bowls, season with pepper and olive oil and serve.