Pound chicken breasts to 1/4-inch thickness. In medium bowl, mix frozen spinach and feta and add 1/4 teaspoon salt. Evenly divide mixture and spoon onto chicken breasts.
Close chicken breasts and secure with toothpicks or butcher’s string. Sprinkle remaining seasonings onto chicken. Press the Sauté button and add coconut oil to Instant Pot. Sear each chicken breast until golden brown (this may take two batches). Press the Cancel button.
Remove chicken and set aside briefly. Pour water into Instant Pot and scrape bottom to remove any chicken or seasoning that is stuck on. Place steam rack into pot.
Place chicken on steam rack and click lid closed. Press ‘Pressure Cook’ and adjust time for 15 minutes. When timer beeps, allow a 15-minute natural release, then quick-release the remaining pressure. Serve warm with favorite white sauce if desired.