Season chicken and brown in a pan. Transfer chicken to pressure cooker and set to "slow cook". Add chicken stock, butter, onions, garlic, thyme, and cover with glass lid. Adjust time for 2 hrs.
Remove lid and carefully stir in the orzo pasta. Cover with lid and cook for another 20 minutes.
Open the cooker and remove the chicken. Spoon out the orzo. Garnish with parsley and serve.