Hello,
This is a table form Leo Dictionary which would help you identify where der/das is used for "Schnitzel". As you can see, in all the cases, "Schnitzel" can take "das", but only in three ways mentioned here, it can take "der" - which is when it is used to mean a chip, a scrap, or a shred. But even in these three cases, you can use "das" as well.
Hope this helps.