Begin by cutting the boneless skinless chicken breasts into bite-sized pieces.
In a mixing bowl, whisk together the chicken stock, pineapple juice, ketchup, soy sauce, rice vinegar, honey, and pepper to create the sauce.
Set your pressure cooker to the sauté function. Add a splash of oil if desired, and toss in the yellow onion wedges. Sauté for about 2-3 minutes until they begin to soften. Then, add the green bell pepper and cook for another minute.
Add the bite-sized chicken pieces to the pot with the sautéed vegetables. Pour the sauce mixture over the chicken and stir well to combine.
Close the lid of your pressure cooker and ensure the valve is set to sealing. Cook on high pressure for 8 minutes. Allow a natural release for 5 minutes, then carefully switch to quick release to release any remaining steam.
In a small bowl, mix the cornstarch with cold water to create a slurry. Set the pressure cooker back to the sauté function, and stir in the slurry. Cook for 2-3 minutes until the sauce thickens to your desired consistency.
Spoon the sweet and sour chicken over a bed of rice or noodles, and garnish with sesame seeds or chopped green onions if desired. Enjoy your delicious, homemade Pressure Cooker Sweet and Sour Chicken!