Your fajitas need sauce.
I had Italian Beef (from Portillo's) for supper, one sandwich on the Turano French bread they supply with their make-at-home kit (beef, gravy, peppers and bread), one sandwich on a Banh Mi roll.
The Turano roll held up better when I put the gravy on, but they bake them specifically for Portillo's, and I have heard from others who've made their own Italian Beef that getting bread that doesn't completely fall apart when wet is harder than getting the beef/gravy right. (A good slicer is a must, though, the beef has to be sliced really thin.)