1) Heat the oil in a large saucepan, add the onions, and fry gently, covered, for 10 minutes. Add the chilli to the onion, along with the garlic, cumin, and turmeric. Crush the cardamom pods, and add to the saucepan. Stir and let cook for a moment or two, then add the lentils and pour in 2 cups of water. Bring to a boil, cover, and simmer gently for 20-30 minutes, or until the lentils are very soft.
2) When the lentils are nearly done, wash the spinach thoroughly in 2-3 changes of water and remove any tough stems. Put the spinach into a dry saucepan and cook over moderately high heat until the leaves have wilted and the spinach is tender and much reduced in size - about 7 minutes. Drain well in a colander. Add the spinach to the lentils, mixing well and season with salt and pepper. Serve the dal at once or reheat when needed; it's also very good the next day.