The turrets he lays down do not autotarget champions anymore. Thus you can abuse the same mechanic you use to poke champions under the main turrets. Hit and step out before the turret fires on u. There is a small window but its there.
Also the item
Shuts dongers down by reducing all their damage by 20% and giving you MR and HP to reduce it further. Like I said he's easy to beat its just you need more game knowledge.
Also you prob need champion knowedge on Donger himself. If you had played him and learned his weaknesses you would know he can only put out about 7 or 8 turrets early. 3 at the start free, and the rest will be based on his cd of his Q. Thus if you take them out one by one only getting in range to hit and retreat without being in range of the other 2 then you take out his sustained damage. By the time the 7th or 8th turret comes out, Donger will be being pushed back in lane from the minon wave alone. As he by himself with no turrets, clears waves slower than shaco in lane.
I suggest to beat donger start these Items

on your first back get these

If your still behind after that.... well the donger isn't the problem... I'd suggest going to bots. Bc 2 things counter AP damage which is all he has. thats HP and MR... You just got HP and MR and are on the way to your Adptive Helm. The doron shield early actually heals more damage than a turret shot does from his turrets plus boost your hp and hp regen along with giving u 5 damage vs minions. So theres no excuse to lose lane.