Turn Instant Pot to saute, wait until it reads "hot" and then add oil. Let the oil heat for a minute or two.
Season the chicken well with salt and pepper and add to the Instant Pot (it may be easier to do this in two batches). Cook for about 2 minutes per side, just until no longer pink.
Add red pepper, green pepper, onion, pineapple, ginger, garlic, salt and pepper flakes and cook 1 minute.
Whisk together the 1 cup pineapple juice, brown sugar, ketchup and vinegar. Pour over chicken and stir.
Put the lid on, turn the valve to sealing, and select Manual or Pressure Cook for a cook time of 2 minutes.
When the cook time is up, open the valve slowly to release the pressure.
Whisk together the corn starch and water.
Turn the Instant Pot to saute and stir in the corn starch slurry. Cook for 1-2 minutes until thickened. Taste and adjust seasonings to taste. Serve.
