To begin, soak the chana dal for half an hour. Boil it with salt, turmeric powder, and 1 tsp oil until almost cooked. It should still have a bite not be mushy. Drain and keep aside. Save the liquid.
Peel and dice the lauki (bottle gourd) into cubes. Soak them in water so that they don't colorize.
Heat 2 tbsp of oil in a pan. Add in a bay leaf. Add the achari masala - mustard seeds, cumin seeds, fennel seeds, fenugreek seeds, and nigella seeds. Allow them to crackle.
Add in finely chopped onions and chopped green chillies. Saute until the onions are translucent.
Add in ginger garlic paste. Saute until the onions colorize. Do not brown.
Next, add finely chopped tomatoes. Mix well. Add the salt. This helps tomatoes cook faster. Cook until the tomatoes soften.
Now add in the dry masalas - Kashmiri red chilli powder, cumin powder, coriander powder, and turmeric powder. Mix well.
Add a bit of water. Cover with a lid and cook until the oil starts appearing on the sides.
Next, add the diced lauki. Mix well and saute for a few minutes. Add 1/2 cup water. Cover and cook until the lauki is tender.
Now add in the boiled chana dal and tamarind pulp. Saute. Add some leftover water from the dal you boiled. Cover and cook until done.
Finally, add garam masala powder. Mix well. Adjust the gravy as per your taste.
For the tempering, heat oil in a tadka pan. Add in cumin seeds, whole red chillies, and curry leaves. As they begin to crackle, pour this tadka over the dal.
The Achari Lauki Chana Dal is ready to serve. Garnish with chopped coriander leaves. Serve hot with puris or parathas.