This version of the Steak Sandwich is excellent, you will hardly notice the difference from the original one! It is very different though in content of fat, carbs, GI and is definately way more diet friendly. So just because you decided to cut back a little doesn't mean that you have to miss out on the taste or even the experience. I have even offered these rolls for my clients' events, when I was catering, whenever they requested healthy options! Everyone asked for the recipe afterwards.
Give it a taste and see for yourself.
If you do not wish to go full low carb then use a whole wheat bagette instead.
An excellent idea to use leftover steaks.