You don’t have to use ciabatta rolls, but choose something hearty. I love ciabatta because the vinaigrette really seeps down into all the nooks and crannies of the bread. And be sure to choose a good, soft mozzarella cheese. You’ll probably have to look in the specialty cheese department of your grocery store. Enjoy! Once you try it, I’m sure it will become a weekly quick dinner in your house as well!
In a small bowl, whisk the balsamic, mustard, Italian seasoning and sugar until combined. Salt and pepper to taste. Slowly whisk in the olive oil. Brush the cut sides of each ciabatta roll, top and bottom, with the vinaigrette. Layer tomatoes, mozzarella and basil leaves. Drizzle the remaining vinaigrette (to taste) on top of the basil leaves. Serve immediately.
https://simplycleanandfitmom.com/2014/04/caprese-sandwich-with-balsamic-vinaigrette/