Make the teriyaki sauce by mixing soy sauce, pineapple juice, honey, rice vinegar, garlic, ginger, and red pepper flakes in a small bowl. Set it aside to add to the dish later.

Use the sauté button on the Instant Pot, add oil, and let it heat briefly. While the oil is heating, lightly season the chicken with salt and pepper on each side. Put the seasoned chicken in a single layer in the heated oil (do it in batches if necessary to avoid overcrowding), and sear the chicken on each side for 2 minutes or until it turns golden. Once the chicken is fully seared, take it out of the pot and place it on a plate. Turn off the sauté function by pressing cancel.

Pour ¼ cup of water into the pot and scrape up the browned bits from the bottom. Put the chicken back in the pot and pour the prepared teriyaki sauce over it.

Cover the Instant Pot with the lid and make sure the vent knob is sealed. Cook on HIGH pressure for 7 minutes by pressing manual/pressure cook and adjusting the time to 7 minutes using the +/- buttons.

After the cooking time, let the pressure release naturally for at least 10 minutes. After 10 minutes, release any remaining pressure quickly if desired, or let the pressure release fully on its own.

Open the lid, take out the chicken, and place it on a clean plate. Press cancel on the Instant Pot to turn off the keep warm function. Then, press sauté to bring the sauce to a simmer.

In a small bowl, mix cornstarch and the remaining ¼ cup of water until completely dissolved. Whisk the cornstarch mixture into the Instant Pot and let it cook for two to three minutes, stirring occasionally, until the sauce thickens. Once thickened, press cancel to turn off the Instant Pot.

Serve the chicken with the thickened sauce, and if you like, garnish with sesame seeds and green onions.