Set Instant Pot to sauté and allow to preheat for 2 minutes.
Add oil to pot and swirl gently to coat.
Add onion and garlic; sauté 4 minutes.
Stir in garam masala and cayenne pepper; cook until fragrant, stirring constantly, about 30 seconds.
Drain juice from one can of tomatoes; stir in both cans of tomatoes, plus the chickpeas and salt.
Cover Instant Pot and fasten lid; set steam valve to sealing.
Set to high pressure for 10 minutes (the pot should take 15–20 minutes to come to pressure).
When cooking is finished, quick-release the pressure by turning the steam valve to venting.
Remove the lid and stir in the coconut milk.
Serve the chickpea mixture over rice; garnish with cilantro, if desired.
