In a large pot, heat some cooking oil over medium heat. Sauté the chopped onions for 2 minutes until soft.
Add the sliced trumpet mushroom stems and sauté for another minute. Cover the pot and cook for about 5 minutes.
Remove the lid and sprinkle turmeric, salt, and nutmeg. Stir well.
Add the tomato paste and soaked green split peas. Stir for a minute, then add the water.
Pierce the dried lemons (limo amani) with a sharp knife or fork, then toss them into the pot along with the cinnamon stick and cardamom pods (in a tea sachet or cloth for easy removal).
Bring the mixture to a boil, then reduce the heat and simmer for 35-45 minutes. Adjust the seasoning at the end.
Remove the cinnamon stick and cardamom pods at the end.