Turn the IP to 'Saute' mode in the 'More' setting.
While the IP starts to heat, prepare the ground coconut paste. In a mixer or food processor, add the the ground coconut and water and grind it until it just comes together. Do not aim for a smooth paste, leave it coarse. Keep this aside.
Add the coconut oil, followed by the chopped red onions, the finely chopped garlic and the slit green chilies.
Stir for around 2 minutes. Then add the chopped tomatoes and stir for another minute, until the tomatoes start to soften. Add the turmeric, coriander powder and cumin and stir.
Add the ground coconut paste, and mix it well with the rest of the ingredients in the IP. Then add the tamarind water or tamarind paste and mix well.
Add the curry leaves and stir. Add the coconut milk and mix well to combine.
Add the prawns and mix well.
Put on the lid of the IP, and with the vent in 'sealing' position, switch to 'Pressure Cook' mode, in 'Low Pressure' setting. Set the time for 2 minutes. Let the prawns cook. Once done, the IP will beep. Do a 'Quick Release' ie, turn the valve from sealing to venting position to release the steam quickly.
Open the lid, add the salt to season the shrimp curry, and mix it well. Serve the Goan prawn curry with some steamed rice.