Add ½ cup freshly squeezed orange juice, 1 tablespoon fresh orange zest, 5 cloves garlic, ¼ cup low-sodium soy sauce, ½ packed cup light brown sugar, ¼ cup freshly squeezed lemon juice, and 1 teaspoon grated fresh ginger (if using) to medium mixing bowl. Whisk ingredients together until fully incorporated. Set aside.
Set Instant Pot to Sauté mode. Add 1 tablespoon neutral oil, distributing oil across bottom of Instant Pot insert. Heat oil until shimmering, then add 2 pounds boneless, skinless chicken breasts and sprinkle ¼ teaspoon salt over.
Stir to incorporate ingredients, then sauté chicken 2 minutes, stirring occasionally, until chicken is just opaque around edges.
Add orange glaze mixture to Instant Pot and stir to incorporate.
Secure lid on Instant Pot with vent in Sealing position. Set Instant Pot to Manual High Pressure for 5 minutes. Instant Pot will pressurize, then 5-minute cook time will begin.
Meanwhile, add 3 tablespoons cornstarch and 3 tablespoons water to small bowl. Whisk ingredients together vigorously until fully combined. Set aside.
When 5-minute cook time ends, carefully Quick Release pressure and remove Instant Pot lid. Use caution - any escaping steam will be very hot.
Set Instant Pot to Sauté mode. Pour cornstarch slurry into Instant Pot and stir to incorporate. Continue stirring 2 to 3 minutes or until sauce has thickened.
Once sauce has thickened, portion chicken and sauce into serving bowls with cooked white rice. Garnish each serving with thinly sliced green onions and thin orange slices if desired. Serve immediately.