To a pressure cooker add the washed lentils, add 2.5 cups water, 1/2 teaspoon salt and 1/4 teaspoon turmeric powder. Cook at high flame for 2 whistles, then lower the flame and cook for another 7-8 minutes or till lentils are completely cooked. Let the pressure of the cooker come off on it's own. Set aside. In case you don't have a pressure cooker, cook the lentils in a pan till completely cooked.
Heat oil in a pan on medium heat. Once the oil is hot, add cumin seeds and mustard seeds. Wait till cumin seeds crackle and mustard seeds start popping out.
Once the seeds start crackling, add chopped garlic and green chili. Saute for a minute or till garlic just starts turning golden brown in color.
Add chopped tomatoes, salt and cook for 2 minutes. We don't want to overcook the tomatoes here.
Add chopped spinach and mix. Cook for 2-3 minutes or till there's no raw smell of tomatoes or spinach.
Add the cooked dal to the pan and let it all come to a boil. Lower the heat, add more water if needed (I did add 1/4 water here) and let the dal simmer for 5 minutes.
Check the salt and adjust to taste. Sprinkle garam on top and remove pan from heat.
Squeeze in some fresh lemon juice and serve spinach dal with any bread or steamed rice!