To make the marinade, in a small bowl or measuring cup, whisk together the tamari, sesame oil, vinegar, and ginger. Place the chicken breasts in a shallow pan or baking dish and pour the marinade over the top. Cover with plastic wrap and marinate in the refrigerator for at least 30 minutes and up to 2 hours, turning occasionally to coat.
Select Sauté on the Instant Pot® and heat the oil. Working in batches, add the chicken breasts, reserving the marinade, and brown evenly on both sides, 2–3 minutes per side. Add the stock and use a wooden spoon to scrape up any browned bits. Add the reserved marinade and stir to combine. Press the Cancel button to reset the program.
Lock the lid in place and turn the valve to Sealing. Press the Pressure Cook button and set the cook time for 6 minutes at high pressure.
Meanwhile, to make the dressing, put the vinegar, tamari, brown sugar, ginger, pepper, and canola oil in a blender or food processor and blend until smooth. Set aside.
When the chicken has finished cooking, let the steam release naturally for 5 minutes, before turning the valve to Venting to quick-release any residual steam.
Carefully remove the lid and use tongs to transfer the chicken to a plate. Let the meat cool slightly and then shred it with two forks.
Divide the rice, lettuce, cabbage, chicken, oranges, and peanuts evenly among 4 plates. Serve with dressing alongside.