Heat 2tsp oil in a small saute pan and fry chana dal, coriander seeds and red chilies until dal is lightly browned and fragrant, about 2-3 minutes. Remove into a bowl.
To the same pan, add onions and fry until browned around the edges. Remove from the pan and let cool slightly.
Grind the chana dal mixture until smooth. Add onions, tamarind paste, grated coconut and salt; grind until smooth. Set aside.
To make the Curry:
(Optional) To remove some bitterness from bittergourd, microwave it with some salt and 1tbsp tamarind paste for 5-6 minutes ot until the veggie is almost cooked and tender. Squeeze out the liquid and use as needed.
Heat 1tbsp oil in a saute pan, add the chopped bittergourd and fry until it turns golden, about 8-10 minutes. Add the ground masala paste, mix well and cook for 4-5 minutes. This curry should be dry, so don’t add any water.