soak tamarind in warm water ( 1 cup), squeeze and take out the clean extract and keep aside.
Take a wok, add oil, when it gets heated up add methi seeds add all the dals and chillies and saute until a nice aroma comes out of it and they would have changed colour too.
Then add the diced squash and saute it for few minutes with the curry leaves, Keep the stove in a low flame, add a tsp of salt and close the lid the vegetable will cook fast.
Once the vegetables are evenly cooked add the tamarind juice, add some more water and allow it boil for some minutes, until the raw smell seizes.
Add 2 to 3 tsp of Rasam Powder allow it to boil for few more minutes, If it is becoming very thick add more water, add jaggery and allow it boil, for 2 to 3 minutes.
If u find the sambhar is very watery, Take a tbsp of rice powder dilute it in water and pour it into the sambhar, within minutes the sambhar gets thickens.
Serve it with hot rice & a tsp of oil