In the Instant Pot, combine the onions, tomatoes, 1/4 cup of the water, the oil, ginger, garlic, turmeric, garam masala, and cayenne. Stir well to combine.
Secure the lid on the pot. Close the pressure-release valve. Select MANUAL or PRESSURE COOK and set the pot at HIGH pressure for 5 minutes. At the end of the cooking time, allow the pot to rest undisturbed for 5 minutes, then release any remaining pressure.
Select SAUTÉ. Add the remaining 1/2 cup water, the paneer, cream, cilantro, and peas. Cook, stirring occasionally, until heated through, 5 to 8 minutes. Select CANCEL.