Start the instant pot in saute mode and heat oil in it. Add mustard seeds, red chili whole and curry leaves.
When the mustard seeds start to splutter, add chopped onion and saute for 2 minutes.
Add tomatoes, salt, turmeric powder and cayenne.
Add the lentils and water. Stir well. Press Cancel and close the instant pot lid with vent in sealing position.
Press Manual or Pressure Cook mode for 3 minutes. When the instant pot beeps, do a quick pressure release.
Open the lid and add mango pieces. Simmer for 2 minutes until the dal starts boiling.
Garnish with cilantro and Mango Dal is ready to be served.
You can use only toor dal or only masoor or equal quantities of both. If using another dal, the cooking time may vary.
I suggest to add mango to the lentils you will use up within the day. Storing lentils with mango added will change the flavor. It is okay to cook the lentils to refrigerate, and add mango when you are ready to consume it.
If using unripe mango, then add it along with the lentils when pressure cooking. Increase the pressure cook time to 5 mins and no simmering required later.