Turn on the Instant Pot and set to Saute mode. Once it's heated, add in oil, mustard seeds, cumin seeds and curry leaves.
Once they start to sizzle, add in the garlic, ginger and chopped onions. Fry for a few minutes, stirring occasionally, until the onions start to brown.
Add in the spices and give it a quick mix. Add in chopped tomatoes and let it cook for a couple of minutes until the tomatoes start to soften and pulp.
Mix in the lentils and water, and let it come to a quick boil.
Add in the tamarind paste, season with salt and stir well to combine.
Put on the lid and set the Instant Pot to manual Pressure Cook mode for 5 minutes, making sure that the valve in on the sealing position.
Let the pressure release naturally before removing the lid. Give it a good stir and garnish with cilantro leaves before serving.