Turn your Instant Pot to the sauté setting and add the oil. If your Instant Pot has a temperature change function, turn it to medium-high heat. Add the chicken and cook for 4-5 minutes, or until browned, stirring occasionally.
Add the ginger and garlic, stir, and cook for 30 seconds or until aromatic. Stir in 3/4 cup of the orange juice, rice vinegar, brown sugar, soy sauce, sriracha, red pepper flakes, and orange zest. Scrape up the bits on the bottom of the pot if needed.
Close the lid and cook for 4 minutes on high pressure. Let the pressure release naturally for 5 minutes, then quick release the rest.
Turn your Instant Pot to the sauté setting. In a small bowl, whisk the remaining orange juice with the cornstarch. Once the sauce is bubbling, start mixing in the cornstarch slurry, 1 tbsp at a time, until you've reached your desired consistency.
Turn the heat off, garnish with green onion, and serve.