Melt butter in a frypan over medium heat. Fry the zucchini in butter until browned and slightly tender. Season with chilli flakes, salt and pepper, and stir in the pasta sauce. Cook and stir until sauce is heated.
Spoon a generous amount of the zucchini mixture into each bread roll. Top with a handful of grated mozzarella. Close the rolls, and wrap individually in aluminium foil.
Bake for 15 minutes in the preheated oven, until bread is heated through and cheese is melted.