I think Haggis was definitely on the right track saying "slices". Listel/listell/listelle is an architectural term which can denote a thin trim or border, or can refer to planks or tiles (oblong or square) on the floor. I tried several dictionaries and could not find one with a food related definition.
I would have to guess that in this case (having watched pizza made with sliced cheese) that it would mean to slice the mozzarella and then lay it out over the surface like planks or tiles.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain