1. Add the chicken, soy sauce, and ketchup to the Instant Pot. Give everything a quick stir.
2. Cover the pot with the lid, and make sure that the valve is in sealing position. Press MANUAL or PRESSURE COOK (depending on which Instant Pot you have) and cook on high for three minutes.
3. Allow the Instant Pot to come to pressure (about 10 minutes), after which it will begin counting the three minutes of cooking time. When it beeps, quickly release the steam by turning the vent to RELEASE position away from your face.
4. Carefully remove the lid and press the SAUTE setting. Add the brown sugar and sesame oil.
5. To thicken the sauce, make a cornstarch slurry: Combine two tablespoons cornstarch with one tablespoon water. Add it to the sauce and stir with a wooden spoon until the sauce thickens. Switch off the sauté setting.
6. Serving suggestion: Top with additional sesame seeds and sliced scallions. Serve over rice.