Place soy sauce, sugar, vinegar, red pepper flakes, garlic, ginger and chicken in Instant Pot. Close and Seal Instant Pot and turn the venting knob to SEALING.
Press PRESSURE COOK on new models or MANUAL on older models and cook on high for 5 minutes. The Instant Pot will takes a few minutes to come to pressure then begin counting time.
Once the Instant Pot has finished cooking the chicken and beeps, allow to naturally release pressure for at least 5 minutes. Flip seal to ‘release’ to ensure pressure has released then open and remove chicken to rest before shredding with forks.
Meanwhile, press SAUTE on the Instant Pot and let the liquid reduce and the flavors concentrate. After liquid has reduced by ¼, combine corn starch with water and stir in.
Whisk frequently while boiling until thick enough to coat a spoon. Add shredded chicken back to the Instant Pot. Stir until coated with homemade teriyaki sauce and heated through.
Serve with additional sauce, sliced scallions, sesame seeds, hot sauce and/or fresh cilantro.
To cook Instant Pot Teriyaki Chicken from frozen simply increase the cook time to 15 minutes on high pressure. Decrease the amount of soy sauce to ¼ cup and water to 2 tablespoons. To make in a slow cooker, simply place all ingredients except cornstarch and water in the slow cooker and cook on low 3-4 hours or 2-3 hours on high. Stir in cornstarch/water mix the last 45 minutes of cooking.