Prepare the Swiss chard: Separate the individual Swiss chard leaves and wash them thoroughly. Cut out the thick stems, including where they still extend into the leaf. Cut the stems into pieces about 1–1.5 cm (½ inch) wide and finely chop the leaves into strips about 0.5–1 cm (¼–½ inch) wide. Set the stems and leaves aside separately.
Sauté the onion: Peel and finely dice the onion. Heat oil in a pot and sauté the onion over medium heat until translucent.
Add the Swiss chard stems: Add the chopped Swiss chard stems and sauté for 2–3 minutes.
Prepare the garlic and ginger: Peel the garlic and ginger, finely chop or pulse in a food processor, and add to the pot. Sauté briefly.
Toast the spices: Add the chili, turmeric, cumin, and coriander powder and stir well. Toast the spices for about 1 minute over medium heat until they are fragrant—but do not let them burn.
Add the tomatoes: Finely chop the tomatoes or pulse them in a food processor. Add them to the pot along with the salt and sauté for about 3–5 minutes. Stir occasionally.
Add the lentils and Swiss chard leaves: Add the finely chopped chard leaves and yellow lentils, then pour in the vegetable stock. Stir everything, cover, well and let it simmer for 10 minutes. Stir occasionally.
Stir in the coconut milk: Add the coconut milk and let the curry simmer for another 5–10 minutes (uncovered), until the lentils are tender and the curry is creamy and thick.
Adjust the consistency: If your chard curry becomes too thick, add a little water or additional vegetable stock, stir well, and let it simmer briefly. Season to taste: Stir in lemon juice, freshly ground black pepper, and finely chopped cilantro leaves.
Serve: Serve the curry with cooked rice, for example. I also like to season it with soy sauce and top it with even more cilantro.