Pressure cook the dal and turmeric until the dal is soft and mashable. You can also do this on a stovetop. Cover the dal with an inch of water, bring to a boil, cover and simmer until soft, about 45 minutes to an hour. Add water if the dal gets dry.
Heat 1 tsp oil and add to it the coriander seeds, chana dal, fenugreek seeds, and red chillies. Saute, stirring frequently, until the coriander seeds and dal are a couple of shades darker. Don't let anything burn.
Remove the coriander seeds mixture to a blender, add the coconut and enough water to make a smooth paste. Blend.
Place the tamarind extract in a saucepan with 1 cup of water or, if you used the tamarind pods, place the pulp you extracted in a saucepan.
Add some salt and bring the mixture to a boil. Add the curry leaves.
Add the pumpkin cubes, return to a boil, cover, lower heat to a simmer, and let the pumpkin cook until it's almost tender, about 8-10 minutes.
Add the ground masala, increase heat, and bring the mixture to a boil.
Add the cooked dal and sambar powder and stir well. Add more water if needed.
When the dal comes to a boil, lower the heat once again and simmer for about 10 minutes. Add water if the sambar gets too dry. You want a fairly fluid texture.
Heat the remaining 1 tsp of oil and add the mustard seeds and asafetida. When the mustard crackles, pour the oil over the dal and mix well.
Serve hot with rice.