Place chicken breasts in the Instant Pot.
Whisk ketchup, sriracha, honey, soy sauce, and water in a bowl until smooth. Pour the mixture over the chicken.
Close the lid and set the valve to "sealing". Cook on high pressure for 10 minutes.
Perform a quick pressure release once the countdown finishes.
Remove the chicken and place it on a cutting board.
Press the "sauté" button on the Instant Pot. Mix cornstarch and 1/4 cup cold water in a small bowl or measuring cup. Add the mixture to the Instant Pot and simmer for a few minutes until the sauce thickens.
Meanwhile, cut the chicken into bite-sized pieces. Return the chicken to the Instant Pot once the sauce has thickened.
Serve over rice, optionally garnished with chopped scallions.