Soak tamarind in 1 cup of water and get thick juice.
Steam and cook the pumpkin in a idli cooker. NOTE: should cook pumpkin without adding water.
Roast in oil coriander seeds, split bengal gram, split black gram, dry chili, cumin seed. Cool this to room temperature and grind them along with coconut into a coarse paste by adding 3 tablespoon (tbsp.) of water.
Cook the pigeon pea by adding water until they submerge in a pressure cooker or 15 minutes in a pan. Add turmeric powder, cooked pumpkin and bring to boil in high heat for 3 minutes.
Reduce heat now add the tamarind juice, salt as needed and continue cooking for 1 minute.
Now add the ground paste, 1/4 cup of water and bring to boil. Cook for 2 minutes. You can add sugar if you like to.
Now add curry leaf, coriander leaf and boil for 5 minutes.
In a separate pan heat oil, add mustard seeds. Once it stop spattering add to the boiling sambar.