Dry chicken with paper towels and slice it into 1-2 inch chunks. I prefer 2-inch chunks because they keep their shape better.
In a medium bowl, whisk together all the ingredients listed under Sauce Mix. Whisk to combine and add red pepper flakes, if you want to add some heat to the dish. Set aside.
Heat up your pressure cooker: press Sauté -> click on the Adjust button -> select More to get the Sauté More function, which means that the food will be sautéed over medium-high heat. Wait for the Instant Pot indicator to read HOT.
Add the oil to the hot Instant Pot, add the chicken and sauté for 3-4 minutes, stirring a few times. Cook until it just starts to look white on the outside. When sautéing it, stir constantly so it doesn't stick to the bottom of the pan.
Also, after you sauté the chicken, check if bits stuck to the bottom, in that case, deglaze the pot with 1/4 cup water and scrape them with a wooden spoon. If you leave the bits stuck to the bottom, they may burn or cause the pot not to come to pressure.
Add the Sauce Mix to the pot over the chicken. Gently stir to combine the chicken with the sauce.
Close lid, select the Poultry function and adjust the time to 5 minutes on High Pressure. Or just select Manual, and select 5 minutes on High Pressure.
Use a 10-minute Natural Release. Turn off the heat. Release the remaining pressure. Open the lid.
Select again the Sauté function, on LOW.
In a medium bowl combine 2 tablespoons of cornstarch with the pineapple juice, whisk until all combined with no lumps.
Add the mixture to the Instant Pot and gently stir to combine. Cook on Sauté function for a few more minutes, stirring gently, until the sauce thickens.
If you want the sauce even thicker, mix one more tablespoon of cornstarch with juice and add it to the pot.
Let the chicken stand for 5-7 minutes, the sauce will thicken more.
Serve over rice and garnish with fresh chopped green onions and extra lemon zest.