In a small bowl whisk together the soy sauce, rice wine vinegar, brown sugar, garlic, ginger and red pepper flakes. Set aside.
Sprinkle 1 tbsp of cornstarch and pepper over the chicken and toss well, making sure each pieces of chicken is coated in cornstarch.
Turn the Instant Pot to the "Saute" setting and add the sesame oil and olive oil. Once the oil is hot, add the chicken pieces and brown for 3 minutes. Press "Cancel" on your IP.
Pour the sauce over the chicken and stir so that all the chicken is coated evenly. Close the lid on the Instant Pot, turn the valve to "Sealing" and cook on "Manual/High Pressure" for 6 minutes.
Turn the valve to "Venting" to do a quick release, wait fort the IP to depressurize. When it's safe, remove the lid. Whisk the remaining 1 tbsp of cornstarch with the 2 tbsp of water to make a slurry, then stir it in with the chicken. Add the cashews and stir everything together.
Turn the Instant Pot to the "Saute" setting and cook for an additional 1 to 2 minutes until sauce thickens.
Sprinkle with green onions and sesame seeds and serve over rice.