You can reduce the sugar to half but I highly recommend keeping some, to balance out the saltiness from the soy sauce.

Thanks for leaving a positive review and pointing out the cooking time. The cooking usually happens very fast when heating up the pan very hot. When I was using my carbon steel pan, I feel like by the time I flipped all the chicken pieces, they are already done. But I do think the 15 to 20 seconds description is not accurate, since I probably spent longer than that to flip the chicken. I tweaked the language and hope now it’s better.

Oyster sauce works great in a brown sauce. You can check out the sauce in this recipe: https://omnivorescookbook.com/chicken-and-broccoli/ It uses oyster sauce so you don’t need as much sugar, but you still need some to balance the flavor. If you’re very concerned about sugar, you can reduce the sugar in half but I wouldn’t skip it completely.
For the tenderizing, I would use 1/2 teaspoon baking soda instead (I’ve not used kiwi to tenderize smaller pieces of meat before so I don’t know how it perform in a stir fry recipe. I’m afraid the meat might fall apart too easily). The baking soda method is great in stir fries and it helps browning the meat better too. Before cooking, make sure to drain all the marinating liquid to prevent splattering. If the chicken takes a while to brown to properly release from the pan, I would even consider only cooking on side (if the top has almost turned white when you’re browning the bottom). Because the chicken will keep cooking after you cook it with the sauce. If you ended up making it, please do let me know how it goes because I’m very interested to see if the recipe works well in a stainless steel pan.