|>>|| No. 13298
You're overcooking them. 170 for 35 seems only slightly excessive, 30 should do it. You could invest in a meat thermometer to check when they're at a safe temperature. I would recommend cooking it at a higher temperature for a shorter time, though, 220 for 20ish minutes is likely better, the higher heat will crisp the outside rather than slowly rendering it and should avoid the toughness.
>Maybe brine soak would be something to try but it seems silly to salt up an otherwise healthy protein.
This is deeply concerning to me. Salt is not bad for you unless you have medical conditions what would make it so, and if you're not putting salt on your food, it's going to be shit no matter what you do. Brining is an excellent idea and will pretty much guarantee very moist chicken breasts.
Even if you don't brine them, you should at least be whacking a bit of salt and pepper on them before you put them in the oven - this itself will act as a sort of brine and reduce the rubberyness of the outer meat too.