Heat olive oil in a large pot over medium heat. Add onions and sauté until soft and caramelised.
Add lentils, potatoes, vegetable stock and cumin. Bring to a boil, then reduce heat and simmer for 20 minutes.
Add chopped spinach or Swiss chard leaves to the pot and continue simmering until the lentils are tender and the chard is wilted, about 15 minutes.
Add the lemon juice & season with salt and pepper to taste. Serve hot with lemon wedges.
