Preheat oven to 350F and line a baking sheet with parchment paper.
Fry up ham steaks over medium heat until browned on each side. While they are cooking, slice rolls in half and spread on pesto, as desired (a little goes a long way!).
Place ham steaks on rolls and then layer with sliced mozzarella.
Add back the top of the rolls and brush with melted butter.
Bake the sandwiches for at least 18-20 minutes to melt the cheese and toast the tops.