In a small bowl, combine onion powder, garlic powder, dried oregano, dried thyme, salt, and pepper.
Place chicken on a cutting board, loosely cover with plastic wrap and use a meat mallet to pound to an even thinness.
Pat chicken dry with paper towel, then rub with the spice blend, evenly coating both sides of all pieces.
Add 1 tablespoon of olive oil to the Instant Pot insert and set to sauté mode. When oil is heated, add chicken breasts and brown them on both sides. Transfer chicken to a plate and set aside.
Add the remaining olive oil to the Instant Pot insert, scraping the bottom with a wooden spoon. Add mushrooms and cook a few minutes, then stir in the garlic and cook about 20 seconds.
Switch off the sauté mode and deglaze the Instant Pot insert with a little chicken stock.
Return the chicken to the Instant Pot, and pour on the rest of the chicken stock. Place the lid on, turn the valve to the sealing position, and set to manual pressure / high pressure for 4 minutes.
When done, perform a quick pressure release, open the lid, and remove the chicken.
Set to sauté mode, stir in the heavy cream and parmesan, then simmer for a few minutes until cheese melts and sauce thickens.
To serve, pour the creamy mushroom sauce over the chicken and garnish with fresh thyme or freshly chopped parsley.