Press the Saute button on the Instant Pot and adjust to High. When it reads HOT, add the oil and wait 1 minute, or until shiny.
Fry the curry paste, garlic, ginger, and onions in the hot oil until fragrant and onions are tender (about 5 minutes.)
Add chicken, the rest of the vegetables, pineapples and juice, coconut milk, and cashews. Stir to coat everything in the paste and onion mixture.
Turn OFF saute mode. Place the lid on the Instant Pot, turn the knob to Sealing, and pressure cook on Manual High Pressure for 5 minutes.
Carefully perform a quick release in short bursts until the pin drops on the lid.
Open the lid and stir.
Turn on High Saute to return the curry to a simmer (adjust to low if it boils too rapidly.)
Add 1/4 cup cream of coconut, then taste again. If you'd like it sweeter, add the remaining 1/4 cup. I used 1/2 cup with the entire can of curry paste.
Mix together cornstarch and cold water to make a slurry. While stirring, add in the slurry to the simmering curry to thicken. Add an additional tablespoon of cornstarch slurry at a time to make it as thick as you’d like.
Turn off heat and serve immediately over rice.