Put the dal in a medium-sized pot with 5 cups of water. Bring to a boil, skimming the foam that rises to the top. Once it boils, stir in the turmeric and cover partially, occasionally stirring. Cook for 75 minutes, being careful to check and stir a few times after 60 minutes. Stir in the salt when the dal is done.
While the dal cooks, heat the ghee in a frying pan over medium heat. Add the mustard and cumin seeds. Stir for 30 seconds and then add the onion. Saute 5-6 minutes or until the onion starts to brown.
Add the garlic, ginger, and green chili and cook for another 1-2 minutes.
Add the spinach and 1/2 cup water. Bring to a boil and cover. Cook until the spinach wilts, around 8-10 minutes.
When the dal is done cooking, add the spinach mixture to it and combine. If the dal feels too dry, stir in a bit of water to a consistency of your liking. Adjust salt to taste.