Heat the oil in the Instant Pot or Pressure cooker on saute (medium heat). When the oil is hot, add the mustard seeds, and cook until they start to pop, about 10 seconds. Add the fenugreek seeds, red chiles, and curry leaves carefully, and cook for a few seconds. Add the garlic and onion and cook until translucent, about 5 minutes
Add the sambhar powder, mix, and cook for half a minute. Add tomatoes, turmeric, and mix. Cook until the tomatoes are saucy, 6 to 8 minutes. Add the vegetables and mix in.
Add the drained split peas, salt, tamarind and water. Mix, close the lid and cook for 10 to 15 minutes (longer for split peas). Let the pressure release naturally. Add more tamarind extract if needed. Taste and adjust salt and heat. Add a pinch of sugar to balance the tang if needed. Garnish with cilantro and lemon juice. Serve as a soup or over rice or with dosa crepes or steamed rice cakes(Idli).
Saucepan: Combine the toor dal/ split peas in a saucepan with 4 cups of water and the vegetables. Partially cover, and cook over medium heat until the split peas are very tender, about 30 minutes. Add the salt, and tamarind and mix well. You can mash some of the split peas. Make the tempering from step 1 and 2 to in a skillet. Mix into the simmering split peas. Taste and adjust salt and heat.