It’s not looking promising. It started with the Wish - new menu.
Reports here were the Dream’s options changed. No reason to expect otherwise on the Fantasy. The menu listed for the Magic on the
Disney Cruise Line Blog shows these choices for sandwiches:
View attachment 901112
They might make your BLT if asked. Just like Uncrustables and Mickey Bars are not listed in the menu but are available.
A BLT was my go-to for Room Service.