Place the chicken in the bottom of the Instant Pot. Place the onion on top of the chicken.
In a small bowl combine the brown sugar, ketchup, vinegar, soy sauce, Sriracha, sesame oil, garlic, ginger, and black pepper. Mix well and pour over top of the chicken and onions.
Place the lid on the Instant Pot and press the pressure cook button.
Pressure cook on high for 20 minutes.
Let the pressure release manually for 5 minutes then release the remaining pressure.
Remove the lid and add the broccoli, peppers, and pineapple.
Place the lid back on and hit the pressure cook button. Turn on low pressure and cook for 4 minutes. Release the pressure immediately.
Serve chicken and vegetables over top of rice.