Heat Instant Pot to saute. When it says HOT add oil. Season chicken with salt, pepper, and garlic powder. Add to the pot and cook 1-2 minutes per side, until browned. Add chicken stock and scrape the bottom to prevent burning.
Add mushrooms and onions and garlic cloves. Turn pot to manual pressure cook and set the timer to four minutes. Let cook then naturally release pressure.
While cooking, whisk parmesan cheese into the half and half.
Once pressure is released, open pot and switch to saute again. Remove chicken from the pot and set aside. Add half and half mixture, spinach, and roasted red peppers. Stir well. Let cook 4-5 minutes, or until sauce thickens. Add chicken back in and taste for seasoning. Serve over pasta or rice. Garnish with basil.