Pressure cook tur dal (pigeon peas) in enough water and turmeric powder for 3 to 4 whistles.
Wait for the pressure to release. Mash well and keep aside.
Heat a pan with oil. Add mustard seeds and when it crackles, add broken whole dry red chili, urad dal and roast for few seconds till it turns golden brown
Add onion and sauté till it turns translucent.
Add tomatoes, chopped peerkangai and sauté till they wilt.
Add 1/4 cup water, salt, sambar powder and mix well. (You can also add the water used to cook tur dal if you happen to have in excess).
Close with a lid and let it cook for 2-3 minutes over low flame.
Add mashed dal, more water if needed to get the thick consistency, mix well and let it cook for another 3-4 minutes over low flame.
In a mortar, using the pestle crush the whole pepper corns coarsely and keep it ready. Do this just before adding to the gravy and not before hand, as the flavor of the pepper is very important.
Mix in freshly grated coconut, crushed pepper corns, torn curry leaves and stir well.
Transfer to a serving bowl. Close with a lid and let it rest for 5 minutes for the all the flavors to come together and set.
Peerkangai Oorpu is ready.
You can serve this to mix with rice and enjoy with a side dish or serve this as a side dish to any spicy kulambu sadam as a kootu.