Subway normally asks if you want it toasted after the meat is added to the sandwich. I’m sure they’ll toast a plain bun (and maybe I’ll try asking for that next time for a tuna sandwich). The most crazy toasting I’ve done at Subway is asking for a meatball sub to be toasted after they put on tomatoes and the cheese, not before.
That said, my first Yumbo was better than a second Yumbo two weeks later, kind of like McRibs taste good after a long absence but not so much a week later. I wonder if BK will do a McRib-style special promotion once a year with the Yumbo.