For a spicier version, add some red pepper flakes to the beef mixture or use spicy Italian sausage instead of ground beef. You can also experiment with different cheeses, such as provolone or fontina, for a unique flavor profile. If you prefer a vegetarian option, substitute the ground beef with sautéed mushrooms and spinach. For a smoky flavor, try using smoked bacon or adding a dash of smoked paprika to the filling.