To make the sauce: In a medium bowl, whisk together 1 tablespoon oil, soy sauce, vinegar, ketchup, honey, garlic, ginger, five-spice powder, and red pepper flakes and set aside.
Add chicken to a sealable plastic bag. Pour in 2 tablespoons cornstarch, salt, and black pepper. Seal top and turn the bag several times to coat chicken.
Add the remaining 1 tablespoon oil to the pressure cooker and turn it on to Sauté. Allow oil to heat up for 1 minute and then add coated chicken. Sear for 2 minutes.
Press the Cancel button and pour sauce into the pressure cooker. Stir to coat chicken with sauce. Place lid on pressure cooker and lock it into place. Set the steam release knob to the Sealing position. Press the Manual button and set to 10 minutes.
In a small bowl, stir to combine remaining 1 tablespoon cornstarch with water until cornstarch is dissolved.
When the cooking cycle has finished, manually release by turning the knob to Venting. Hot steam will be released from the valve in venting mode. Once all steam has been released and pressure valve has lowered, remove the lid. Press the Sauté button and pour the cornstarch mixture into the pressure cooker and whisk into sauce. Add cashews and continue stirring for 1-2 minutes until sauce has thickened. Serve over rice and sprinkle with green onions.