Combine cornstarch and pepper in a resealable plastic bag. Add chicken pieces and shake bag to coat with cornstarch mixture.

Heat oil in skillet over medium-high heat. Brown chicken about 2 minutes on each side. Transfer to a multi-functional pressure cooker (such as Fagor®).

Combine cashews, soy sauce, rice vinegar, ketchup, sweet chili sauce, brown sugar, garlic, ginger, red pepper flakes, and sesame oil in a bowl. Pour over chicken.

Close and lock lid. Select Slow Cook function. Cook on Low until flavors are well combined and chicken is cooked through, about 2 hours. Garnish with green onions.