Set your Instant Pot to Saute setting
Heat oil in the pot. Add cumin and mustard seeds. Cook for about 15 seconds (they will jump around in the pot)
Add the onion and stir. Cook, stirring often, until the onion is soft and translucent.
Add the garlic, ginger-garlic paste, garam masala, coriander and turmeric. Cook for about 45 seconds, until fragrant
Pour the crushed tomatoes in the pot and scrape up any bits stuck to the bottom of the pan.
Add the chickpeas and stir.
Attach the Instant Pot lid (make sure the valve is in the sealing position). Set the pressure level to "Normal" for 15 minutes.
When the timer had finished, release the pressure using the quick release method.
When the pressure has been released, remove the lid and stir the chana masala