Wash and chop the cucumber pieces with skin. Keep it in a bowl. Soak tamarind in required water and take the extract. Set aside.
In a pressure cooker, take the dal, add required water, turmeric powder and little oil. Place a bowl inside the cooker and keep the chopped cucumber pieces. No need to add water. Close the cooker.
Pressure cook for one whistle in low flame. Open the cooker after the steam is released.
Heat oil in a small kadai. Roast all the ingredients given under " to roast and grind" till golden and aromatic. Grind everything to a smooth paste adding grated coconut.
In a bowl, take the tamarind extract, ground masala paste, cooked toor dal, turmeric powder, salt, jaggery and cooked cucumber pieces. Mix well and check the consistency. Add more water if needed.
Boil the sambar for few minutes till raw smell of tamarind goes away. Switch off the flame and garnish with coriander leaves. Temper in ghee and add to the gravy. Mix well and serve with plain rice.
Notes
You can use chow chow / Chayote or mixed vegetables instead of cucumber.
Make sure the cucumber pieces are not over cooked. No need to add water in the bowl that you place inside the cooker.
You can also add little sambar powder for variations.